TY - JOUR AB - Following the rapid, but independent, diffusion of X-ray spectral and phase-contrast systems, this work demonstrates the first combination of spectral and phase-contrast computed tomography (CT) obtained by using the edge-illumination technique and a CdTe small-pixel (62 μm) spectral detector. A theoretical model is introduced, starting from a standard attenuation-based spectral decomposition and leading to spectral phase-contrast material decomposition. Each step of the model is followed by quantification of accuracy and sensitivity on experimental data of a test phantom containing different solutions with known concentrations. An example of a micro CT application (20 μm voxel size) on an iodine-perfusedex-vivomurine model is reported. The work demonstrates that spectral-phase contrast combines the advantages of spectral imaging, i.e. high-Z material discrimination capability, and phase-contrast imaging, i.e. soft tissue sensitivity, yielding simultaneously mass density maps of water, calcium, and iodine with an accuracy of 1.1%, 3.5%, and 1.9% (root mean square errors), respectively. Results also show a 9-fold increase in the signal-to-noise ratio of the water channel when compared to standard spectral decomposition. The application to the murine model revealed the potential of the technique in the simultaneous 3D visualization of soft tissue, bone, and vasculature. While being implemented by using a broad spectrum (pink beam) at a synchrotron radiation facility (Elettra, Trieste, Italy), the proposed experimental setup can be readily translated to compact laboratory systems including conventional X-ray tubes. AU - Brombal, L.* AU - Arfelli, F.* AU - Brun, F.* AU - Di Trapani, V.* AU - Endrizzi, M.* AU - Menk, R.* AU - Perion, P.* AU - Rigon, L.* AU - Saccomano, M. AU - Tromba, G.* AU - Olivo, A.* C1 - 70262 C2 - 55475 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Edge-illumination spectral phase-contrast tomography. JO - Phys. Med. Biol. VL - 69 IS - 7 PB - Iop Publishing Ltd PY - 2024 SN - 0031-9155 ER - TY - JOUR AB - Objective. For fast neutron therapy with mixed neutron and gamma radiation at the fission neutron therapy facility MEDAPP at the research reactor FRM II in Garching, no clinical dose calculation software was available in the past. Here, we present a customized solution for research purposes to overcome this lack of three-dimensional dose calculation. Approach. The applied dose calculation method is based on two sets of decomposed pencil beam kernels for neutron and gamma radiation. The decomposition was performed using measured output factors and simulated depth dose curves and beam profiles in water as reference medium. While measurements were performed by applying the two-chamber dosimetry method, simulated data was generated using the Monte Carlo code MCNP. For the calculation of neutron dose deposition on CT data, tissue-specific correction factors were generated for soft tissue, bone, and lung tissue for the MEDAPP neutron spectrum. The pencil beam calculations were evaluated with reference to Monte Carlo calculations regarding accuracy and time efficiency. Main results. In water, dose distributions calculated using the pencil beam approach reproduced the input from Monte Carlo simulations. For heterogeneous media, an assessment of the tissue-specific correction factors with reference to Monte Carlo simulations for different tissue configurations showed promising results. Especially for scenarios where no lung tissue is present, the dose calculation could be highly improved by the applied correction method. Significance. With the presented approach, time-efficient dose calculations on CT data and treatment plan evaluations for research purposes are now available for MEDAPP. AU - Sommer, L.B.* AU - Kampfer, S.* AU - Chemnitz, T.* AU - Breitkreutz, H.* AU - Combs, S.E. AU - Wilkens, J.J.* C1 - 69996 C2 - 55355 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Pencil beam kernel-based dose calculations on CT data for a mixed neutron-gamma fission field applying tissue correction factors. JO - Phys. Med. Biol. VL - 69 IS - 4 PB - Iop Publishing Ltd PY - 2024 SN - 0031-9155 ER - TY - JOUR AB - Objective.The range uncertainty in proton radiotherapy is a limiting factor to achieve optimum dose conformity to the tumour volume. Ionoacoustics is a promising approach forin siturange verification, which would allow to reduce the size of the irradiated volume relative to the tumour volume. The energy deposition of a pulsed proton beam leads to an acoustic pressure wave (ionoacoustics), the detection of which allows conclusion about the distance between the Bragg peak and the acoustic detector. This information can be transferred into a co-registered ultrasound image, marking the Bragg peak position relative to the surrounding anatomy.Approach.A CIRS 3D abdominal phantom was irradiated with 126 MeV protons at a clinical proton therapy centre. Acoustic signals were recorded on the beam axis distal to the Bragg peak with a Cetacean C305X hydrophone. The ionoacoustic measurements were processed with a correlation filter using simulated filter templates. The hydrophone was rigidly attached to an ultrasound device (Interson GP-C01) recording ultrasound images of the irradiated region.Main results.The time of flight obtained from ionoacoustic measurements were transferred to an ultrasound image by means of an optoacoustic calibration measurement. The Bragg peak position was marked in the ultrasound image with a statistical uncertainty ofσ= 0.5 mm of 24 individual measurements depositing 1.2 Gy at the Bragg peak. The difference between the evaluated Bragg peak position and the one obtained from irradiation planning (1.0 mm) is smaller than the typical range uncertainty (≈4 mm) at the given penetration depth (10 cm).Significance.The measurements show that it is possible to determine the Bragg peak position of a clinical proton beam with submillimetre precision and transfer the information to an ultrasound image of the irradiated region. The dose required for this is smaller than that used for a typical irradiation fraction. AU - Schauer, J.* AU - Wieser, H.P.* AU - Lascaud, J.* AU - Huang, Y. AU - Vidal, M.* AU - Herault, J.* AU - Ntziachristos, V. AU - Dollinger, G.* AU - Parodi, K.* C1 - 67904 C2 - 54382 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Range verification of a clinical proton beam in an abdominal phantom by co-registration of ionoacoustics and ultrasound. JO - Phys. Med. Biol. VL - 68 IS - 12 PB - Iop Publishing Ltd PY - 2023 SN - 0031-9155 ER - TY - JOUR AB - This Roadmap paper covers the field of precision preclinical x-ray radiation studies in animal models. It is mostly focused on models for cancer and normal tissue response to radiation, but also discusses other disease models. The recent technological evolution in imaging, irradiation, dosimetry and monitoring that have empowered these kinds of studies is discussed, and many developments in the near future are outlined. Finally, clinical translation and reverse translation are discussed. AU - Verhaegen, F.* AU - Butterworth, K.T.* AU - Chalmers, A.J.* AU - Coppes, R.P.* AU - De Ruysscher, D.* AU - Dobiasch, S. AU - Fenwick, J.D.* AU - Granton, P.V.* AU - Heijmans, S.H.J.* AU - Hill, M.A.* AU - Koumenis, C.* AU - Lauber, K.* AU - Marples, B.* AU - Parodi, K.* AU - Persoon, L.C.G.G.* AU - Staut, N.* AU - Subiel, A.* AU - Vaes, R.D.W.* AU - van Hoof, S.* AU - Verginadis, I.L.* AU - Wilkens, J.J.* AU - Williams, K.J.* AU - Wilson, G.D.* AU - Dubois, L.J.* C1 - 68150 C2 - 53602 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Roadmap for precision preclinical x-ray radiation studies. JO - Phys. Med. Biol. VL - 68 IS - 6 PB - Iop Publishing Ltd PY - 2023 SN - 0031-9155 ER - TY - JOUR AB - PURPOSE: We present a microscopic mechanism that accounts for the outward burst of ``cold" ion species (IS) in a high-energy particle track due to coupling with ''hot" non-ion species (NIS). IS refers to radiolysis products of ionized molecules, whereas NIS refers to non-ionized excitations of molecules in a medium. The interaction is mediated by a quantized field of acoustic phonons, a channel that allows conversion of thermal energy of NIS to kinetic energy of IS, a flow of heat from the outer to the inner core of the track structure. METHODS: We perform Monte Carlo (MC) simulations of ionizing radiation track structures in water to score the spatial coordinates and energy depositions that form IS and NIS at atto-second time scales. We calculate temperature profiles of the tracks with MC track structure simulations and verify the results analytically using the Rutherford scattering formulation. These temperature profiles are then used as boundary conditions in a series of multi-scale atomistic molecular dynamic (MD) simulations that describe the sudden expansion and enhanced diffusive broadening of tracks initiated by the non-equilibrium spectrum of high-energy IS. RESULTS: We demonstrate the coexistence of ``hot" NIS with ``cold" IS in the radiation track structures right after their generation. NIS, concentrated within nano-scales volumes wrapping around IS, are the main source of intensive heat-waves and the outward burst of IS due to femto-second time scale IS-NIS coupling. By comparing the transport of IS coupled to NIS with identical configurations of non-interacting IS in thermal equilibrium at room temperature, we demonstrate that the energy gain of IS due to the surrounding hot nanoscopic volumes of NIS significantly increases their effective diffusion constants. CONCLUSIONS: The much higher diffusion constants predicted in the present model suggest higher inter-track chemical reaction rates at FLASH-UHDR, as well as lower intra-track reaction rates. AU - Abolfath, R.M.* AU - Baikalov, A.* AU - Bartzsch, S. AU - Afshordi, N.* AU - Mohan, R.* C1 - 64880 C2 - 52576 TI - The effect of non-ionizing excitations on the diffusion of ion species and inter-track correlations in FLASH ultra-high dose rate radiotherapy. JO - Phys. Med. Biol. VL - 67 IS - 10 PY - 2022 SN - 0031-9155 ER - TY - JOUR AB - Objective. In clinical positron emission tomography (PET) imaging, quantification of radiotracer uptake in tumours is often performed using semi-quantitative measurements such as the standardised uptake value (SUV). For small objects, the accuracy of SUV estimates is limited by the noise properties of PET images and the partial volume effect. There is need for methods that provide more accurate and reproducible quantification of radiotracer uptake. Approach. In this work, we present a deep learning approach with the aim of improving quantification of lung tumour radiotracer uptake and tumour shape definition. A set of simulated tumours, assigned with 'ground truth' radiotracer distributions, are used to generate realistic PET raw data which are then reconstructed into PET images. In this work, the ground truth images are generated by placing simulated tumours characterised by different sizes and activity distributions in the left lung of an anthropomorphic phantom. These images are then used as input to an analytical simulator to simulate realistic raw PET data. The PET images reconstructed from the simulated raw data and the corresponding ground truth images are used to train a 3D convolutional neural network. Results. When tested on an unseen set of reconstructed PET phantom images, the network yields improved estimates of the corresponding ground truth. The same network is then applied to reconstructed PET data generated with different point spread functions. Overall the network is able to recover better defined tumour shapes and improved estimates of tumour maximum and median activities. Significance. Our results suggest that the proposed approach, trained on data simulated with one scanner geometry, has the potential to restore PET data acquired with different scanners. AU - Dal Toso, L.* AU - Chalampalakis, Z.* AU - Buvat, I.* AU - Comtat, C.* AU - Cook, G.* AU - Goh, V.* AU - Schnabel, J.A. AU - Marsden, P.K.* C1 - 64955 C2 - 52232 TI - Improved 3D tumour definition and quantification of uptake in simulated lung tumours using deep learning. JO - Phys. Med. Biol. VL - 67 IS - 9 PY - 2022 SN - 0031-9155 ER - TY - JOUR AB - Objective. Dual energy computed tomography (DECT) has been shown to provide additional image information compared to conventional CT and has been used in clinical routine for several years. The objective of this work is to present a DECT implementation for a Small Animal Radiation Research Platform (SARRP) and to verify it with a quantitative analysis of a material phantom and a qualitative analysis with an ex-vivo mouse measurement. Approach. For dual energy imaging, two different spectra are required, but commercial small animal irradiators are usually not optimized for DECT. We present a method that enables dual energy imaging on a SARRP with sequential scanning and an Empirical Dual Energy Calibration (EDEC). EDEC does not require the exact knowledge of spectra and attenuation coefficients; instead, it is based on a calibration. Due to the SARRP geometry and reconstruction algorithm, the calibration is done using an artificial CT image based on measured values. The calibration yields coefficients to convert the measured images into material decomposed images. Main results. To analyze the method quantitatively, the electron density and the effective atomic number of a material phantom were calculated and compared with theoretical values. The electron density showed a maximum deviation from the theoretical values of less than 5% and the atomic number of slightly more than 6%. For use in mice, DECT is particularly useful in distinguishing iodine contrast agent from bone. A material decomposition of an ex-vivo mouse with iodine contrast agent was material decomposed to show that bone and iodine can be distinguished and iodine-corrected images can be calculated. Significance. DECT is capable of calculating electron density images and effective atomic number images, which are appropriate parameters for quantitative analysis. Furthermore, virtual monochromatic images can be obtained for a better differentiation of materials, especially bone and iodine contrast agent. AU - Duda, M.A.* AU - Grad, A.* AU - Kampfer, S.* AU - Dobiasch, S. AU - Combs, S.E. AU - Wilkens, J.J.* C1 - 65592 C2 - 52377 TI - Dual energy CT for a small animal radiation research platform using an empirical dual energy calibration. JO - Phys. Med. Biol. VL - 67 IS - 13 PY - 2022 SN - 0031-9155 ER - TY - JOUR AB - Objective Proton therapy is gaining popularity because of the improved dose delivery over conventional radiation therapy. The secondary dose to healthy tissues is dominated by secondary neutrons. Commercial rem-counters are valuable instruments for the on-line assessment of neutron ambient dose equivalent (H*(10)). In general, however, a priori knowledge of the type of facility and of the radiation field is required for the proper choice of any survey meter. The novel Mevion S250i Hyperscan synchrocyclotron mounts the accelerator directly on the gantry. It provides a scanned 227 MeV proton beam, delivered in pulses with a pulse width of 10 µs at 750 Hz frequency, which is afterwards degraded in energy by a range shifter modulator system. This environment is particularly challenging for commercial rem-counters; therefore, we tested the reliability of some of the most widespread rem-counters to understand their limits in the Mevion S250i stray neutron field. Approach This work, promoted by the European Radiation Dosimetry Group (EURADOS), describes a rem-counter intercomparison at the Maastro Proton Therapy centre in the Netherlands, which houses the novel Mevion S250i Hyperscan system. Several rem-counters were employed in the intercomparison (LUPIN, LINUS, WENDI-II, LB6411, NM2B-458, NM2B-495Pb), which included simulation of a patient treatment protocol employing a water tank phantom. The outcomes of the experiment were compared with models and data from the literature. Main results We found that only the LUPIN allowed for a correct assessment of H*(10) within a 20% uncertainty. All other rem-counters underestimated the reference H*(10) by factors from 2 to more than 10, depending on the detector model and on the neutron dose per pulse. In pulsed fields, the neutron dose per pulse is a fundamental parameter, while the average neutron dose rate is a secondary quantity. An average 150-200 µSv/GyRBE neutron H*(10) at various positions around the phantom and at distances between 186 cm and 300 cm from it was measured per unit therapeutic dose delivered to the target. Significance Our results are partially in line with results obtained at similar Mevion facilities employing passive energy modulation. Comparisons with facilities employing active energy modulation confirmed that the neutron H*(10) can increase up to more than a factor of 10 when passive energy modulation is employed. The challenging environment of the Mevion stray neutron field requires the use of specific rem-counters sensitive to high-energy neutrons (up to a few hundred MeV) and specifically designed to withstand pulsed neutron fields. AU - Zorloni, G.* AU - Bosmans, G.* AU - Brall, T. AU - Caresana, M.* AU - De Saint-Hubert, M.* AU - Domingo, C.* AU - Ferrante, C.* AU - Ferrulli, F.* AU - Kopec, R.* AU - Leidner, J.* AU - Mares, V. AU - Nabha, R.* AU - Olko, P.* AU - Caballero-Pacheco, M.A.* AU - Rühm, W. AU - Silari, M.* AU - Stolarczyk, L.* AU - Swakon, J.* AU - Tisi, M. AU - Trinkl, S.* AU - van Hoey, O.* AU - Vilches-Freixas, G.* C1 - 64501 C2 - 52240 TI - Joint EURADOS WG9-WG11 rem-counter intercomparison in a Mevion S250i proton therapy facility with Hyperscan pulsed synchrocyclotron. JO - Phys. Med. Biol. VL - 67 IS - 7 PY - 2022 SN - 0031-9155 ER - TY - JOUR AB - The pediatric patients are in the growing stage with more dividing cells than adults. They are greater sensitive to the radiation dose undergoing computed tomography (CT) scanning. It is necessary and essential to assess the absorbed dose and effective dose to children. Monte Carlo simulation with computational phantoms is one of the most used methods for dose calculation in medical imaging and radiotherapy. Because of the vast change of the pediatric body with age increasing, many research groups developed series pediatric phantoms for various ages. However, most of the existing pediatric reference phantoms were developed based on Caucasian populations, which is not conformable to Chinese pediatric patients. The use of different phantoms can contribute a difference in the dose calculation. To assess the CT dose of Chinese pediatric patients more accurately, we developed the Chinese pediatric reference phantoms series, including the 3-month (CRC3m), 1-year-old (CRC01), 5-year-old (CRC05), 10-year-old (CRC10), 15-year-old male (CRCM15), and female (CRCF15) phantoms. Furthermore, we applied them to dose assessment of patients undergoing CT scanning. The GE LightSpeed 16 CT scanner was constructed and the paper presents the detailed process of phantoms development and the establishment of the CT dose database (with X-ray tube voltages of 120, 100, and 80 kVp, with collimators of 20, 10, and 5 mm width, with filters for head and body), compares our results with other results based on different phantoms, and analyzes the CT dose calculation results. It was found that the difference in phantoms' characteristics, organ masses, and positions had a significant impact on the CT dose calculation results. The maximum difference came up to 463% (gonads dose undergoing chest examinations). The results are helpful for the dose optimization of Chinese pediatric patients undergoing CT scanning. The developed phantoms could be applied in dose estimation of other medical modalities. AU - Ma, R.* AU - Qiu, R.* AU - Wu, Z.* AU - Ren, L.* AU - Hu, A.* AU - Li, W.B. AU - Li, J.* C1 - 62894 C2 - 51148 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Development of Chinese mesh-type pediatric reference phantoms series and application in dose assessment of Chinese undergoing computed tomography scanning. JO - Phys. Med. Biol. VL - 66 IS - 19 PB - Iop Publishing Ltd PY - 2021 SN - 0031-9155 ER - TY - JOUR AB - Accurate knowledge of the exact stopping location of ions inside the patient would allow full exploitation of their ballistic properties for patient treatment. The localized energy deposition of a pulsed particle beam induces a rapid temperature increase of the irradiated volume and leads to the emission of ionoacoustic (IA) waves. Detecting the time-of-flight (ToF) of the IA wave allows inferring information on the Bragg peak location and can henceforth be used for in-vivo range verification. A challenge for IA is the poor signal-to-noise ratio at clinically relevant doses and viable machines. We present a frequency-based measurement technique, labeled as ionoacoustic tandem phase detection (iTPD) utilizing lock-in amplifiers. The phase shift of the IA signal to a reference signal is measured to derive the ToF. Experimental IA measurements with a 3.5 MHz lead zirconate titanate (PZT) transducer and lock-in amplifiers were performed in water using 22 MeV proton bursts. A digital iTPD was performed in-silico at clinical dose levels on experimental data obtained from a clinical facility and secondly, on simulations emulating a heterogeneous geometry. For the experimental setup using 22 MeV protons, a localization accuracy and precision obtained through iTPD deviates from a time-based reference analysis by less than 15 mu m. Several methodological aspects were investigated experimentally in systematic manner. Lastly, iTPD was evaluated in-silico for clinical beam energies indicating that iTPD is in reach of sub-mm accuracy for fractionated doses < 5 Gy. iTPD can be used to accurately measure the ToF of IA signals online via its phase shift in frequency domain. An application of iTPD to the clinical scenario using a single pulsed beam is feasible but requires further development to reach <1 Gy detection capabilities. AU - Wieser, H.P.* AU - Huang, Y. AU - Schauer, J.* AU - Lascaud, J.* AU - Wuerl, M.* AU - Lehrack, S.* AU - Radonic, D.* AU - Vidal, M.* AU - Herault, J.* AU - Chmyrov, A. AU - Ntziachristos, V. AU - Assmann, W.* AU - Parodi, K.* AU - Dollinger, G.* C1 - 63847 C2 - 51668 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Experimental demonstration of accurate Bragg peak localization with ionoacoustic tandem phase detection (iTPD). JO - Phys. Med. Biol. VL - 66 IS - 24 PB - Iop Publishing Ltd PY - 2021 SN - 0031-9155 ER - TY - JOUR AB - The lowest possible energy of proton scanning beam in cyclotron proton therapy facilities is typically between 60 and 100 MeV. Treatment of superficial lesions requires a pre-absorber to deliver doses to shallower volumes. In most of the cases a range shifter (RS) is used, but as an alternative solution, a patient-specific 3D printed proton beam compensator (BC) can be applied. A BC enables further reduction of the air gap and consequently reduction of beam scattering. Such pre-absorbers are additional sources of secondary radiation. The aim of this work was the comparison of RS and BC with respect to out-of-field doses for a simulated treatment of superficial paediatric brain tumours. EURADOS WG9 performed comparative measurements of scattered radiation in the Proteus C-235 IBA facility (Cyclotron Centre Bronowice at the Institute of Nuclear Physics, CCB IFJ PAN, Krakow, Poland) using two anthropomorphic phantoms-5 and 10 yr old-for a superficial target in the brain. Both active detectors located inside the therapy room, and passive detectors placed inside the phantoms were used. Measurements were supplemented by Monte Carlo simulation of the radiation transport. For the applied 3D printed pre-absorbers, out-of-field doses from both secondary photons and neutrons were lower than for RS. Measurements with active environmental dosimeters at five positions inside the therapy room indicated that the RS/BC ratio of the out-of-field dose was also higher than one, with a maximum of 1.7. Photon dose inside phantoms leads to higher out-of-field doses for RS than BC to almost all organs with the highest RS/BC ratio 12.5 and 13.2 for breasts for 5 and 10 yr old phantoms, respectively. For organs closest to the isocentre such as the thyroid, neutron doses were lower for BC than RS due to neutrons moderation in the target volume, but for more distant organs like bladder-conversely-lower doses for RS than BC were observed. The use of 3D printed BC as the pre-absorber placed in the near vicinity of patient in the treatment of superficial tumours does not result in the increase of secondary radiation compared to the treatment with RS, placed far from the patient. AU - Wochnik, A.* AU - Stolarczyk, L.* AU - Ambrozova, I.* AU - Davidkova, M.* AU - De Saint-Hubert, M.* AU - Domanski, S.* AU - Domingo, C.* AU - Knezevic, Z.* AU - Kopec, R.* AU - Kuć, M.* AU - Majer, M.* AU - Mojzeszek, N.* AU - Mares, V. AU - Martínez-Rovira, I.* AU - Caballero-Pacheco, M.A.* AU - Pyszka, E.* AU - Swakon, J.* AU - Trinkl, S. AU - Tisi, M. AU - Harrison, R.* AU - Olko, P.* C1 - 61356 C2 - 49833 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Out-of-field doses for scanning proton radiotherapy of shallowly located paediatric tumours-a comparison of range shifter and 3D printed compensator. JO - Phys. Med. Biol. VL - 66 IS - 3 PB - Iop Publishing Ltd PY - 2021 SN - 0031-9155 ER - TY - JOUR AB - In the last 25 years microbeam radiation therapy (MRT) has emerged as a promising alternative to conventional radiation therapy at large, third generation synchrotrons. In MRT, a multi-slit collimator modulates a kilovoltage x-ray beam on a micrometer scale, creating peak dose areas with unconventionally high doses of several hundred Grays separated by low dose valley regions, where the dose remains well below the tissue tolerance level. Pre-clinical evidence demonstrates that such beam geometries lead to substantially reduced damage to normal tissue at equal tumour control rates and hence drastically increase the therapeutic window. Although the mechanisms behind MRT are still to be elucidated, previous studies indicate that immune response, tumour microenvironment, and the microvasculature may play a crucial role. Beyond tumour therapy, MRT has also been suggested as a microsurgical tool in neurological disorders and as a primer for drug delivery.The physical properties of MRT demand innovative medical physics and engineering solutions for safe treatment delivery. This article reviews technical developments in MRT and discusses existing solutions for dosimetric validation, reliable treatment planning and safety. Instrumentation at synchrotron facilities, including beam production, collimators and patient positioning systems, is also discussed. Specific solutions reviewed in this article include: dosimetry techniques that can cope with high spatial resolution, low photon energies and extremely high dose rates of up to 15 000 Gy s(-1), dose calculation algorithms-apart from pure Monte Carlo Simulations-to overcome the challenge of small voxel sizes and a wide dynamic dose-range, and the use of dose-enhancing nanoparticles to combat the limited penetrability of a kilovoltage energy spectrum. Finally, concepts for alternative compact microbeam sources are presented, such as inverse Compton scattering set-ups and carbon nanotube x-ray tubes, that may facilitate the transfer of MRT into a hospital-based clinical environment.Intensive research in recent years has resulted in practical solutions to most of the technical challenges in MRT. Treatment planning, dosimetry and patient safety systems at synchrotrons have matured to a point that first veterinary and clinical studies in MRT are within reach. Should these studies confirm the promising results of pre-clinical studies, the authors are confident that MRT will become an effective new radiotherapy option for certain patients. AU - Bartzsch, S. AU - Corde, S.* AU - Crosbie, J.C.* AU - Day, L.* AU - Donzelli, M.* AU - Krisch, M.* AU - Lerch, M.* AU - Pellicioli, P.* AU - Smyth, L.M.L.* AU - Tehei, M.* C1 - 57911 C2 - 48088 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Technical advances in x-ray microbeam radiation therapy. JO - Phys. Med. Biol. VL - 65 IS - 2 PB - Iop Publishing Ltd PY - 2020 SN - 0031-9155 ER - TY - JOUR AB - In our paper (Rabus et al 2019) we presented a procedure to determine the dose enhancement factors (DEFs) for gold nanoparticles (GNPs) for an extended photon radiation field from simulations with narrow beam geometries. In the context of different work, it has become evident that there has been an error in the ROOT software routine used for processing the simulation data for the purpose of our article. More precisely, in the command line where the deposited energy obtained from the simulation was converted to the energy density in the spherical shells used for scoring, the volume of the spherical shells was implemented as (Formula Presented) Using integers in the factor 4/3 in the first bracket leads to an integer output, i.e. 1 instead of 1.3333… In consequence, the values shown as simulation results in figure 5 of our paper were enhanced by a factor of 4/3 and so were the values for the dose enhancement factors for an extended photon field in figures 6 and 7. The corrected figures are presented below. Furthermore, we noted the following typos in the article: • A wrong sign in the denominator on the right-hand side of equation (4). The correct expression is (Formula Presented). In producing the data for figures 7 and 9, the correct equation as given above was used, however. • In the paragraph on page 7 below equation (12), it should read ‘… is on the order of 1/3 (µr)2. … z in equation (11) …’ • In the Conclusion, the second recommendation should read ‘… as given in equation (8). …’ Correcting the identified data processing error leads to a reduction of the predicted DEF for GNPs irradiated with an extended field of diagnostic x-rays by a factor of ¾. In consequence, the conclusions of our publication (regarding the magnitude of the DEFs for an extended beam and the limited radial range where significant DEFs occur) remain.(Figure Presented). AU - Rabus, H.* AU - Gargioni, E.* AU - Li, W.B. AU - Nettelbeck, H.* AU - Villagrasa, C.* C1 - 59994 C2 - 49002 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Erratum: Determining dose enhancement factors of high-Z nanoparticles from simulations where lateral secondary particle disequilibrium exists (Physics in Medicine and Biology (2019)64 (155016) DOI: 10.1088/1361-6560/ab31d4). JO - Phys. Med. Biol. VL - 65 IS - 15 PB - Iop Publishing Ltd PY - 2020 SN - 0031-9155 ER - TY - JOUR AB - Recently, the Task Group 103 of the International Commission on Radiological Protection (ICRP) has developed new mesh-type reference computational phantoms (MRCPs) for adult male and female. When compared to the current voxel-type reference computational phantoms in ICRP Publication 110, the MRCPs have several advantages, including deformability which makes it possible to create phantoms in different body sizes or postures. In the present study, the MRCPs were deformed to produce a set of percentile-specific phantoms representing the 10th, 50th and 90th percentiles of standing height and body weight in Caucasian population. For this, anthropometric parameters for the percentile-specific phantoms were first derived from the anthropometric software and survey data. Then, the MRCPs were modified to match the derived anthropometric parameters. For this, first, the MRCPs were scaled in the axial direction to match the head height, torso length, and leg length. Then, the head, torso, and legs were scaled in the transversal directions to match the lean body mass for the percentile-specific phantoms. Finally, the scaled phantoms were manually adjusted to match the body weight and the remaining anthropometric parameters (upper arm, waist, buttock, thigh, and calf circumferences and sagittal abdominal diameter). The constructed percentile-specific phantoms and the MRCPs were implemented into the Geant4 Monte Carlo code to calculate organ doses for a cesium-137 contaminated floor. The results showed that organ doses of the 50th percentile (both standing height and body weight) phantoms are very dose to those of the MRCPs. There were noticeable differences in organ doses, however, for the 10th and 90th percentile phantoms when compared with those of the MRCPs. The results of the present study confirm the general intuition that a small person receives higher doses than a large person when exposed to a static radiation field, and organs closer to the source receive higher doses. AU - Lee, H.* AU - Yeom, Y.S.* AU - Nguyen, T.T.* AU - Choi, C.* AU - Han, H.* AU - Shin, B.* AU - Zhang, X.* AU - Kim, C.H.* AU - Chung, B.S.* AU - Zankl, M. C1 - 55103 C2 - 46265 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Percentile-specific computational phantoms constructed from ICRP mesh-type reference computational phantoms (MRCPs). JO - Phys. Med. Biol. VL - 64 IS - 4 PB - Iop Publishing Ltd PY - 2019 SN - 0031-9155 ER - TY - JOUR AB - Nanoparticles (NPs) containing high atomic number (high-Z) materials have been shown to enhance the radiobiological effectiveness of ionizing radiation. This effect is often attributed to an enhancement of the absorbed dose in the vicinity of the NPs, based on Monte Carlo simulations that show a significant local enhancement of the energy deposition on the microscopic scale. The results of such simulations may be significantly biased and lead to a severe overestimation of the dose enhancement if the condition of secondary particle equilibrium is not met in the simulation setup. This current work shows an approach to estimate a 'realistic' dose enhancement from the results of such biased simulations which is based on published photon interaction data and provides a way for correcting biased results. AU - Rabus, H.* AU - Gargioni, E.* AU - Li, W.B. AU - Nettelbeck, H.* AU - Villagrasa, C.* C1 - 56534 C2 - 47090 CY - Temple Circus, Temple Way, Bristol Bs1 6be, England TI - Determining dose enhancement factors of high-Z nanoparticles from simulations where lateral secondary particle disequilibrium exists. JO - Phys. Med. Biol. VL - 64 IS - 15 PB - Iop Publishing Ltd PY - 2019 SN - 0031-9155 ER - TY - JOUR AB - Systematic 3D mapping of out-of-field doses induced by a therapeutic proton pencil scanning beam in a 300 × 300 × 600 mm3 water phantom was performed using a set of thermoluminescence detectors (TLDs): MTS-7 (7LiF:Mg,Ti), MTS-6 (6LiF:Mg,Ti), MTS-N (natLiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti), radiophotoluminescent (RPL) detectors GD-352M and GD-302M, and polyallyldiglycol carbonate (PADC)-based (C12H18O7) track-etched detectors. Neutron and gamma-ray doses, as well as linear energy transfer distributions, were experimentally determined at 200 points within the phantom. In parallel, the Geant4 Monte Carlo code was applied to calculate neutron and gamma radiation spectra at the position of each detector. For the cubic proton target volume of 100 × 100 × 100 mm3 (spread out Bragg peak with a modulation of 100 mm) the scattered photon doses along the main axis of the phantom perpendicular to the primary beam were approximately 0.5 mGy Gy-1 at a distance of 100 mm and 0.02 mGy Gy-1 at 300 mm from the center of the target. For the neutrons, the corresponding values of dose equivalent were found to be ∼0.7 and ∼0.06 mSv Gy-1, respectively. The measured neutron doses were comparable with the out-of-field neutron doses from a similar experiment with 20 MV x-rays, whereas photon doses for the scanning proton beam were up to three orders of magnitude lower. AU - Stolarczyk, L.* AU - Trinkl, S. AU - Romero-Expósito, M.* AU - Mojzeszek, N.* AU - Ambrozova, I.* AU - Domingo, C.* AU - Davidkova, M.* AU - Farah, J.* AU - Klodowska, M.* AU - Knezevic, Z.* AU - Liszka, M.* AU - Majer, M.* AU - Miljanić, S.* AU - Ploc, O.* AU - Schwarz, M.A.* AU - Olko, P.* C1 - 53471 C2 - 44737 TI - Dose distribution of secondary radiation in a water phantom for a proton pencil beam-EURADOS WG9 intercomparison exercise. JO - Phys. Med. Biol. VL - 63 IS - 8 PY - 2018 SN - 0031-9155 ER - TY - JOUR AB - Ultrasound waves propagating in water or soft biological tissue are strongly reflected when encountering the skull, which limits the use of ultrasound-based techniques in transcranial imaging and therapeutic applications. Current knowledge on the acoustic properties of the cranial bone is restricted to far-field observations, leaving its near-field unexplored. We report on the existence of skull-guided acoustic waves, which was herein confirmed by near-field measurements of optoacoustically-induced responses in ex-vivo murine skulls immersed in water. Dispersion of the guided waves was found to reasonably agree with the prediction of a multilayered flat plate model. We observed a skull-guided wave propagation over a lateral distance of at least 3 mm, with a half-decay length in the direction perpendicular to the skull ranging from 35 to 300 μm at 6 and 0.5 MHz, respectively. Propagation losses are mostly attributed to the heterogenous acoustic properties of the skull.. It is generally anticipated that our findings may facilitate and broaden the application of ultrasound-mediated techniques in brain diagnostics and therapy. AU - Estrada, H. AU - Rebling, J. AU - Razansky, D. C1 - 50628 C2 - 42533 CY - Bristol SP - 4728-4740 TI - Prediction and near-field observation of skull-guided acoustic waves. JO - Phys. Med. Biol. VL - 62 IS - 12 PB - Iop Publishing Ltd PY - 2017 SN - 0031-9155 ER - TY - JOUR AB - It is not feasible to define very small or complex organs and tissues in the current voxel-type adult reference computational phantoms of the International Commission on Radiological Protection (ICRP), which limit dose coefficients for weakly penetrating radiations. To address the problem, the ICRP is converting the voxel-type reference phantoms into mesh-type phantoms. In the present study, as a part of the conversion project, the micrometer-thick target and source regions in the alimentary and respiratory tract systems as described in ICRP Publications 100 and 66 were included in the mesh-type ICRP reference adult male and female phantoms. In addition, realistic lung airway models were simulated to represent the bronchial (BB) and bronchiolar (bb) regions. The electron specific absorbed fraction (SAF) values for the alimentary and respiratory tract systems were then calculated and compared with the values calculated with the stylized models of ICRP Publications 100 and 66. The comparisons show generally good agreement for the oral cavity, oesophagus, and BB, whereas for the stomach, small intestine, large intestine, extrathoracic region, and bb, there are some differences (e.g. up to ~9 times in the large intestine). The difference is mainly due to anatomical difference in these organs between the realistic mesh-type phantoms and the simplified stylized models. The new alimentary and respiratory tract models in the mesh-type ICRP reference phantoms preserve the topology and dimensions of the voxel-type ICRP phantoms and provide more reliable SAF values than the simplified models adopted in previous ICRP Publications. AU - Kim, H.S.* AU - Yeom, Y.S.* AU - Nguyen, T.T.* AU - Choi, C.* AU - Han, M.C.* AU - Lee, J.K.* AU - Kim, C.H.* AU - Zankl, M. AU - Petoussi-Henß, N. AU - Bolch, W.E.* AU - Lee, C.* AU - Qiu, R.* AU - Eckermann, K.* AU - Chung, B.S.* C1 - 50569 C2 - 42361 SP - 2132-2152 TI - Inclusion of thin target and source regions in alimentary and respiratory tract systems of mesh-type ICRP adult reference phantoms. JO - Phys. Med. Biol. VL - 62 IS - 6 PY - 2017 SN - 0031-9155 ER - TY - JOUR AB - Re-excision rates for breast cancer lumpectomy procedures are currently nearly 25% due to surgeons relying on inaccurate or incomplete methods of evaluating specimen margins. The objective of this study was to determine if cancer could be automatically detected in breast specimens from mastectomy and lumpectomy procedures by a classification algorithm that incorporated parameters derived from fluorescence lifetime imaging (FLIm). This study generated a database of co-registered histologic sections and FLIm data from breast cancer specimens (N=20) and a support vector machine (SVM) classification algorithm able to automatically detect cancerous, fibrous, and adipose breast tissue. Classification accuracies were greater than 97% for automated detection of cancerous, fibrous, and adipose tissue from breast cancer specimens. The classification worked equally well for specimens scanned by hand or with a mechanical stage, demonstrating that the system could be used during surgery or on excised specimens. The ability of this technique to simply discriminate between cancerous and normal breast tissue, in particular to distinguish fibrous breast tissue from tumor, which is notoriously challenging for optical techniques, leads to the conclusion that FLIm has great potential to assess breast cancer margins. Identification of positive margins before waiting for complete histologic analysis could significantly reduce breast cancer re-excision rates. AU - Phipps, J.E.* AU - Gorpas, D. AU - Unger, J.* AU - Darrow, M.* AU - Bold, R.J.* AU - Marcu, L.* C1 - 52266 C2 - 43899 CY - Bristol TI - Automated detection of breast cancer in resected specimens with fluorescence lifetime imaging. JO - Phys. Med. Biol. VL - 63 IS - 1 PB - Iop Publishing Ltd PY - 2017 SN - 0031-9155 ER - TY - JOUR AB - Fluorescence diffuse optical tomography (fDOT) provides 3D images of fluorescence distributions in biological tissue, which represent molecular and cellular processes. The image reconstruction problem is highly ill-posed and requires regularisation techniques to stabilise and find meaningful solutions. Quadratic regularisation tends to either oversmooth or generate very noisy reconstructions, depending on the regularisation strength. Edge preserving methods, such as anisotropic diffusion regularisation (AD), can preserve important features in the fluorescence image and smooth out noise. However, AD has limited ability to distinguish an edge from noise. We propose a patch-based anisotropic diffusion regularisation (PAD), where regularisation strength is determined by a weighted average according to the similarity between patches around voxels within a search window, instead of a simple local neighbourhood strategy. However, this method has higher computational complexity and, hence, we wavelet compress the patches (PAD-WT) to speed it up, while simultaneously taking advantage of the denoising properties of wavelet thresholding. Furthermore, structural information can be incorporated into the image reconstruction with PAD-WT to improve image quality and resolution. In this case, the weights used to average voxels in the image are calculated using the structural image, instead of the fluorescence image. The regularisation strength depends on both structural and fluorescence images, which guarantees that the method can preserve fluorescence information even when it is not structurally visible in the anatomical images. In part 1, we tested the method using a denoising problem. Here, we use simulated and in vivo mouse fDOT data to assess the algorithm performance. Our results show that the proposed PAD-WT method provides high quality and noise free images, superior to those obtained using AD. AU - Correia, T.* AU - Koch, M. AU - Ale, A.B.F* AU - Ntziachristos, V. AU - Arridge, S.* C1 - 47778 C2 - 39459 CY - Bristol SP - 1452-1475 TI - Patch-based anisotropic diffusion scheme for fluorescence diffuse optical tomography-part 2: Image reconstruction. JO - Phys. Med. Biol. VL - 61 IS - 4 PB - Iop Publishing Ltd PY - 2016 SN - 0031-9155 ER - TY - JOUR AB - It has been well recognized that the presence of a skull imposes harsh restrictions on the use of ultrasound and optoacoustic techniques in the study, treatment and modulation of the brain function. We propose a rigorous modeling and experimental methodology for estimating the insertion loss and the elastic constants of the skull over a wide range of frequencies and incidence angles. A point-source-like excitation of ultrawideband acoustic radiation was induced via the absorption of nanosecond duration laser pulses by a 20 μm diameter microsphere. The acoustic waves transmitted through the skull are recorded by a broadband, spherically focused ultrasound transducer. A coregistered pulse-echo ultrasound scan is subsequently performed to provide accurate skull geometry to be fed into an acoustic transmission model represented in an angular spectrum domain. The modeling predictions were validated by measurements taken from a glass cover-slip and ex vivo adult mouse skulls. The flexible semi-analytical formulation of the model allows for seamless extension to other transducer geometries and diverse experimental scenarios involving broadband acoustic transmission through locally flat solid structures. It is anticipated that accurate quantification and modeling of the skull transmission effects would ultimately allow for skull aberration correction in a broad variety of applications employing transcranial detection or transmission of high frequency ultrasound. AU - Estrada, H. AU - Rebling, J. AU - Turner, J.E. AU - Razansky, D. C1 - 47897 C2 - 39723 CY - Bristol SP - 1932-1946 TI - Broadband acoustic properties of a murine skull. JO - Phys. Med. Biol. VL - 61 IS - 5 PB - Iop Publishing Ltd PY - 2016 SN - 0031-9155 ER - TY - JOUR AB - The purpose of this study is to characterize the stray neutron radiation field in scanning proton therapy considering a pediatric anthropomorphic phantom and a clinically-relevant beam condition. Using two extended-range Bonner sphere spectrometry systems (ERBSS), Working Group 9 of the European Radiation Dosimetry Group measured neutron spectra at ten different positions around a pediatric anthropomorphic phantom irradiated for a brain tumor with a scanning proton beam. This study compares the different systems and unfolding codes as well as neutron spectra measured in similar conditions around a water tank phantom. The ten spectra measured with two ERBSS systems show a generally similar thermal component regardless of the position around the phantom while high energy neutrons (above 20 MeV) were only registered at positions near the beam axis (at 0°, 329° and 355°). Neutron spectra, fluence and ambient dose equivalent, H (*)(10), values of both systems were in good agreement (<15%) while the unfolding code proved to have a limited effect. The highest H (*)(10) value of 2.7 μSv Gy(-1) was measured at 329° to the beam axis and 1.63 m from the isocenter where high-energy neutrons (E  ⩾  20 MeV) contribute with about 53%. The neutron mapping within the gantry room showed that H (*)(10) values significantly decreased with distance and angular position with respect to the beam axis dropping to 0.52 μSv Gy(-1) at 90° and 3.35 m. Spectra at angles of 45° and 135° with respect to the beam axis measured here with an anthropomorphic phantom showed a similar peak structure at the thermal, fast and high energy range as in the previous water-tank experiments. Meanwhile, at 90°, small differences at the high-energy range were observed. Using ERBSS systems, neutron spectra mapping was performed to characterize the exposure of scanning proton therapy patients. The ten measured spectra provide precise information about the exposure of healthy organs to thermal, epithermal, evaporation and intra-nuclear cascade neutrons. This comprehensive spectrometry analysis can also help in understanding the tremendous literature data based rem-counters while also being of great value for general neutron shielding and radiation safety studies. AU - Mares, V. AU - Romero-Expósito, M.* AU - Farah, J.* AU - Trinkl, S. AU - Domingo, C.* AU - Dommert, M. AU - Stolarczyk, L.* AU - van Ryckeghem, L.* AU - Wielunski, M. AU - Olko, P.* AU - Harrison, R.M.* C1 - 48597 C2 - 41202 CY - Bristol SP - 4127-4140 TI - A comprehensive spectrometry study of a stray neutron radiation field in scanning proton therapy. JO - Phys. Med. Biol. VL - 61 IS - 11 PB - Iop Publishing Ltd PY - 2016 SN - 0031-9155 ER - TY - JOUR AB - The reference adult computational phantoms of the international commission on radiological protection (ICRP) described in Publication 110 are voxel-type computational phantoms based on whole-body computed tomography (CT) images of adult male and female patients. The voxel resolutions of these phantoms are in the order of a few millimeters and smaller tissues such as the eye lens, the skin, and the walls of some organs cannot be properly defined in the phantoms, resulting in limitations in dose coefficient calculations for weakly penetrating radiations. In order to address the limitations of the ICRP-110 phantoms, an ICRP Task Group has been recently formulated and the voxel phantoms are now being converted to a high-quality mesh format. As a part of the conversion project, in the present study, the skeleton models, one of the most important and complex organs of the body, were constructed. The constructed skeleton models were then tested by calculating red bone marrow (RBM) and endosteum dose coefficients (DCs) for broad parallel beams of photons and electrons and comparing the calculated values with those of the original ICRP-110 phantoms. The results show that for the photon exposures, there is a generally good agreement in the DCs between the mesh-type phantoms and the original voxel-type ICRP-110 phantoms; that is, the dose discrepancies were less than 7% in all cases except for the 0.03 MeV cases, for which the maximum difference was 14%. On the other hand, for the electron exposures (4 MeV), the DCs of the mesh-type phantoms deviate from those of the ICRP-110 phantoms by up to ∼1600 times at 0.03 MeV, which is indeed due to the improvement of the skeletal anatomy of the developed skeleton mesh models. AU - Yeom, Y.S.* AU - Wang, Z.J.* AU - Nguyen, T.T.* AU - Kim, H.S.* AU - Choi, C.* AU - Han, M.C.* AU - Kim, C.H.* AU - Lee, J.K.* AU - Chung, B.S.* AU - Zankl, M. AU - Petoussi-Henß, N. AU - Bolch, W.E.* AU - Lee, C.* C1 - 49809 C2 - 40962 CY - Bristol SP - 7054-7073 TI - Development of skeletal system for mesh-type ICRP reference adult phantoms. JO - Phys. Med. Biol. VL - 61 IS - 19 PB - Iop Publishing Ltd PY - 2016 SN - 0031-9155 ER - TY - JOUR AB - The objective of this work was to investigate the influence of the definition of blood as a distinct source on organ doses, associated with the administration of a novel radiopharmaceutical for positron emission tomography-computed tomography (PET/CT) imaging-(S)-4-(3-(18)F-fluoropropyl)-L-glutamic acid ((18)F-FSPG). Personalised pharmacokinetic models were constructed based on clinical PET/CT images from five healthy volunteers and blood samples from four of them. Following an identifiability analysis of the developed compartmental models, person-specific model parameters were estimated using the commercial program SAAM II. Organ doses were calculated in accordance to the formalism promulgated by the Committee on Medical Internal Radiation Dose (MIRD) and the International Commission on Radiological Protection (ICRP) using specific absorbed fractions for photons and electrons previously derived for the ICRP reference adult computational voxel phantoms. Organ doses for two concepts were compared: source organ activities in organs parenchyma with blood as a separate source (concept-1); aggregate activities in perfused source organs without blood as a distinct source (concept-2). Aggregate activities comprise the activities of organs parenchyma and the activity in the regional blood volumes (RBV). Concept-1 resulted in notably higher absorbed doses for most organs, especially non-source organs with substantial blood contents, e.g. lungs (92% maximum difference). Consequently, effective doses increased in concept-1 compared to concept-2 by 3-10%. Not considering the blood as a distinct source region leads to an underestimation of the organ absorbed doses and effective doses. The pronounced influence of the blood even for a radiopharmaceutical with a rapid clearance from the blood, such as (18)F-FSPG, suggests that blood should be introduced as a separate compartment in most compartmental pharmacokinetic models and blood should be considered as a distinct source in dosimetric calculations. Hence, blood samples should be included in all pharmacokinetic and dosimetric studies for new tracers if possible. AU - Zvereva, A. AU - Petoussi-Henß, N. AU - Li, W.B. AU - Schlattl, H. AU - Oeh, U. AU - Zankl, M. AU - Graner, F.P.* AU - Hoeschen, C. AU - Nekolla, S.G.* AU - Parodi, K.* AU - Schwaiger, M.* C1 - 49724 C2 - 40890 CY - Bristol SP - 7688-7703 TI - Effect of blood activity on dosimetric calculations for radiopharmaceuticals. JO - Phys. Med. Biol. VL - 61 IS - 21 PB - Iop Publishing Ltd PY - 2016 SN - 0031-9155 ER - TY - JOUR AB - The theory of task-based assessment of image quality is reviewed in the context of imaging with ionizing radiation, and objective figures of merit (FOMs) for image quality are summarized. The variation of the FOMs with the task, the observer and especially with the mean number of photons recorded in the image is discussed. Then various standard methods for specifying radiation dose are reviewed and related to the mean number of photons in the image and hence to image quality. Current knowledge of the relation between local radiation dose and the risk of various adverse effects is summarized, and some graphical depictions of the tradeoffs between image quality and risk are introduced. Then various dose-reduction strategies are discussed in terms of their effect on task-based measures of image quality. AU - Barrett, H.H.* AU - Myers, K.J.* AU - Hoeschen, C. AU - Kupinski, M.A.* AU - Little, M.P.* C1 - 43083 C2 - 35991 CY - Bristol SP - R1-R75 TI - Task-based measures of image quality and their relation to radiation dose and patient risk. JO - Phys. Med. Biol. VL - 60 IS - 2 PB - Iop Publishing Ltd PY - 2015 SN - 0031-9155 ER - TY - JOUR AB - The inversion accuracy in optoacoustic tomography depends on a number of parameters, including the number of detectors employed, discrete sampling issues or imperfectness of the forward model. These parameters result in ambiguities on the reconstructed image. A common ambiguity is the appearance of negative values, which have no physical meaning since optical absorption can only be higher or equal than zero. We investigate herein algorithms that impose non-negative constraints in model-based optoacoustic inversion. Several state-of-the-art non-negative constrained algorithms are analyzed. Furthermore, an algorithm based on the conjugate gradient method is introduced in this work. We are particularly interested in investigating whether positive restrictions lead to accurate solutions or drive the appearance of errors and artifacts. It is shown that the computational performance of non-negative constrained inversion is higher for the introduced algorithm than for the other algorithms, while yielding equivalent results. The experimental performance of this inversion procedure is then tested in phantoms and small animals, showing an improvement in image quality and quantitativeness with respect to the unconstrained approach. The study performed validates the use of non-negative constraints for improving image accuracy compared to unconstrained methods, while maintaining computational efficiency. AU - Ding, L AU - Dean-Ben, X.L. AU - Lutzweiler, C. AU - Razansky, D. AU - Ntziachristos, V. C1 - 46609 C2 - 37665 SP - 6733-6750 TI - Efficient non-negative constrained model-based inversion in optoacoustic tomography. JO - Phys. Med. Biol. VL - 60 IS - 17 PY - 2015 SN - 0031-9155 ER - TY - JOUR AB - In this work we develop a computer-aided diagnosis (CAD) scheme for classification of pulmonary disease for grating-based x-ray radiography. In addition to conventional transmission radiography, the grating-based technique provides a dark-field imaging modality, which utilizes the scattering properties of the x-rays. This modality has shown great potential for diagnosing early stage emphysema and fibrosis in mouse lungs in vivo. The CAD scheme is developed to assist radiologists and other medical experts to develop new diagnostic methods when evaluating grating-based images. The scheme consists of three stages: (i) automatic lung segmentation; (ii) feature extraction from lung shape and dark-field image intensities; (iii) classification between healthy, emphysema and fibrosis lungs. A study of 102 mice was conducted with 34 healthy, 52 emphysema and 16 fibrosis subjects. Each image was manually annotated to build an experimental dataset. System performance was assessed by: (i) determining the quality of the segmentations; (ii) validating emphysema and fibrosis recognition by a linear support vector machine using leave-one-out cross-validation. In terms of segmentation quality, we obtained an overlap percentage (Ω) 92.63 ± 3.65%, Dice Similarity Coefficient (DSC) 89.74 ± 8.84% and Jaccard Similarity Coefficient 82.39 ± 12.62%. For classification, the accuracy, sensitivity and specificity of diseased lung recognition was 100%. Classification between emphysema and fibrosis resulted in an accuracy of 93%, whilst the sensitivity was 94% and specificity 88%. In addition to the automatic classification of lungs, deviation maps created by the CAD scheme provide a visual aid for medical experts to further assess the severity of pulmonary disease in the lung, and highlights regions affected. AU - Einarsdóttir, H.* AU - Yaroshenko, A.* AU - Velroyen, A.* AU - Bech, M.* AU - Hellbach, K.* AU - Auweter, S.* AU - Yildirim, A.Ö. AU - Meinel, F.G.* AU - Eickelberg, O. AU - Reiser, M.* AU - Larsen, R.* AU - ErsbØll, B.K.* AU - Pfeiffer, F.* C1 - 47947 C2 - 39773 CY - Bristol SP - 9253-9268 TI - Computer-aided diagnosis of pulmonary diseases using X-ray darkfield radiography. JO - Phys. Med. Biol. VL - 60 IS - 24 PB - Iop Publishing Ltd PY - 2015 SN - 0031-9155 ER - TY - JOUR AB - The dose coefficients for the eye lens reported in ICRP 2010 Publication 116 were calculated using both a stylized model and the ICRP-110 reference phantoms, according to the type of radiation, energy, and irradiation geometry. To maintain consistency of lens dose assessment, in the present study we incorporated the ICRP-116 detailed eye model into the converted polygon-mesh (PM) version of the ICRP-110 reference phantoms. After the incorporation, the dose coefficients for the eye lens were calculated and compared with those of the ICRP-116 data. The results showed generally a good agreement between the newly calculated lens dose coefficients and the values of ICRP 2010 Publication 116. Significant differences were found for some irradiation cases due mainly to the use of different types of phantoms. Considering that the PM version of the ICRP-110 reference phantoms preserve the original topology of the ICRP-110 reference phantoms, it is believed that the PM version phantoms, along with the detailed eye model, provide more reliable and consistent dose coefficients for the eye lens. AU - Nguyen, T.T.* AU - Yeom, Y.S.* AU - Kim, H.S.* AU - Wang, Z.J.* AU - Han, M.C.* AU - Kim, C.H.* AU - Lee, J.K.* AU - Zankl, M. AU - Petoussi-Henß, N. AU - Bolch, W.E.* AU - Lee, C.* AU - Chung, B.S.* C1 - 47173 C2 - 39132 SP - 8695-8707 TI - Incorporation of detailed eye model into polygon-mesh versions of ICRP-110 reference phantoms. JO - Phys. Med. Biol. VL - 60 IS - 22 PY - 2015 SN - 0031-9155 ER - TY - JOUR AB - Abundant studies have focused on the radiosensitization effect of gold nanoparticles (GNPs) in the cellular environment with x-ray irradiation. To better understand the physical foundation and to initially study the molecular radiosensitization effect within the nucleus, a simple cell model with detailed DNA structure in the central nucleus was set up and complemented with different distributions of single and multiple GNPs in this work. With the biophysical Monte Carlo simulation code PARTRAC, the radiosensitization effects on both physical quantities and primary biological responses (DNA strand breaks) were simulated. The ratios of results under situations with GNPs compared to those without GNPs were defined as the enhancement factors (EFs). The simulation results show that the presence of GNP can cause a notable enhancement effect on the energy deposition within a few micrometers from the border of GNP. The greatest upshot appears around the border and is mostly dominated by Auger electrons. The enhancement effect on the DNA strand breakage becomes smaller because of the DNA distribution inside the nucleus, and the corresponding EFs are between 1 and 1.5. In the present simulation, multiple GNPs on the nucleus surface, the 60 kVp x-ray spectrum and the diameter of 100 nm are relatively more effective conditions for both physical and biological radiosensitization effects. These results preliminarily indicate that GNP can be a good radiosensitizer in x-ray radiotherapy. Nevertheless, further biological responses (repair process, cell survival, etc) need to be studied to give more accurate evaluation and practical proposal on GNP's application in clinical treatment. AU - Xie, W.Z. AU - Friedland, W. AU - Li, W.B. AU - Li, C.Y.* AU - Oeh, U. AU - Qiu, R.* AU - Li, J.L.* AU - Hoeschen, C. C1 - 46446 C2 - 37534 SP - 6195-6212 TI - Simulation on the molecular radiosensitization effect of gold nanoparticles in cells irradiated by X-rays. JO - Phys. Med. Biol. VL - 60 IS - 16 PY - 2015 SN - 0031-9155 ER - TY - JOUR AB - Chromophore quantification in optoacoustic tomography is challenging due to signal contributions from strongly absorbing background tissue chromophores and the depth-dependent light attenuation. Herein we present a procedure capable of correcting for wavelength-dependent light fluence variations using a logarithmic representation of the images taken at different wavelengths assisted with a blind unmixing approach. It is shown that the serial expansion of the logarithm of an optoacoustic image contains a term representing the ratio between absorption of the probe of interest and other background components. Under assumptions of tissue-like background absorption variations, this term can be readily isolated with an unmixing algorithm, attaining quantitative maps of photo-absorbing agent distribution. AU - Dean-Ben, X.L. AU - Bühler, A. AU - Razansky, D. AU - Ntziachristos, V. C1 - 31882 C2 - 34845 CY - Bristol SP - 4785-4797 TI - Estimation of optoacoustic contrast agent concentration with self-calibration blind logarithmic unmixing. JO - Phys. Med. Biol. VL - 59 IS - 17 PB - Iop Publishing Ltd PY - 2014 SN - 0031-9155 ER - TY - JOUR AB - Dose constraints based on histograms provide a convenient and widely-used method for informing and guiding radiotherapy treatment planning. Methods of derivation of such constraints are often poorly described. Two non-parametric methods for derivation of constraints are described and investigated in the context of determination of dose-specific cut-points-values of the free parameter (e.g., percentage volume of the irradiated organ) which best reflect resulting changes in complication incidence. A method based on receiver operating characteristic (ROC) analysis and one based on a maximally-selected standardized rank sum are described and compared using rectal toxicity data from a prostate radiotherapy trial. Multiple test corrections are applied using a free step-down resampling algorithm, which accounts for the large number of tests undertaken to search for optimal cut-points and the inherent correlation between dose-histogram points. Both methods provide consistent significant cut-point values, with the rank sum method displaying some sensitivity to the underlying data. The ROC method is simple to implement and can utilize a complication atlas, though an advantage of the rank sum method is the ability to incorporate all complication grades without the need for grade dichotomization. AU - Ebert, M.A.* AU - Gulliford, S.L.* AU - Buettner, F. AU - Foo, K.* AU - Haworth, A.* AU - Kennedy, A.* AU - Joseph, D.J.* AU - Denham, J.W.* C1 - 31863 C2 - 34824 CY - Bristol SP - N101-N111 TI - Two non-parametric methods for derivation of constraints from radiotherapy dose-histogram data. JO - Phys. Med. Biol. VL - 59 IS - 13 PB - Iop Publishing Ltd PY - 2014 SN - 0031-9155 ER - TY - JOUR AB - ICRP Publication 116 on 'Conversion coefficients for radiological protection quantities for external radiation exposures', provides fluence-to-dose conversion coefficients for organ-absorbed doses and effective dose for various types of external exposures (ICRP 2010 ICRP Publication 116). The publication supersedes the ICRP Publication 74 (ICRP 1996 ICRP Publication 74, ICRU 1998 ICRU Report 57), including new particle types and expanding the energy ranges considered. The coefficients were calculated using the ICRP/ICRU computational phantoms (ICRP 2009 ICRP Publication 110) representing the reference adult male and reference adult female (ICRP 2002 ICRP Publication 89), together with a variety of Monte Carlo codes simulating the radiation transport in the body. Idealized whole-body irradiation from unidirectional and rotational parallel beams as well as isotropic irradiation was considered for a large variety of incident radiations and energy ranges. Comparison of the effective doses with operational quantities revealed that the latter quantities continue to provide a good approximation of effective dose for photons, neutrons and electrons for the 'conventional' energy ranges considered previously (ICRP 1996, ICRU 1998), but not at the higher energies of ICRP Publication 116. AU - Petoussi-Henß, N. AU - Bolch, W.E.* AU - Eckerman, K.F.* AU - Endo, A.* AU - Hertel, N.* AU - Hunt, J.* AU - Menzel, H.G.* AU - Pelliccioni, M.* AU - Schlattl, H. AU - Zankl, M. C1 - 31963 C2 - 34915 CY - Bristol SP - 5209-5224 TI - The first ICRP/ICRU application of the male and female adult reference computational phantoms. JO - Phys. Med. Biol. VL - 59 IS - 18 PB - Iop Publishing Ltd PY - 2014 SN - 0031-9155 ER - TY - JOUR AB - Model-based optoacoustic inversion methods are capable of eliminating image artefacts associated with the widely adopted back-projection reconstruction algorithms. Yet, significant image artefacts might also occur due to reflections and scattering of optoacoustically-induced waves from strongly acoustically-mismatched areas in tissues. Herein, we modify the model-based reconstruction methodology to incorporate statistically-based weighting in order to minimize these artefacts. The method is compared with another weighting procedure termed half-image reconstruction, yielding generally better results. The statistically-based weighting is subsequently verified experimentally, attaining quality improvement of the optoacoustic image reconstructions in the presence of acoustic mismatches in tissue phantoms and small animals ex-vivo. AU - Dean-Ben, X.L. AU - Ma, R. AU - Rosenthal, A. AU - Ntziachristos, V. AU - Razansky, D. C1 - 26615 C2 - 32303 SP - 5555-5566 TI - Weighted model-based optoacoustic reconstruction in acoustic scattering media. JO - Phys. Med. Biol. VL - 58 IS - 16 PB - IOP Publishing PY - 2013 SN - 0031-9155 ER - TY - JOUR AB - We propose a novel x-ray fluorescence imaging setup for the in vivo detection of high-Z tracer distributions. The main novel aspect is the use of an analyzer-based, energy-resolved detection method together with a radial, scatter reducing collimator. The aim of this work is to show the feasibility of this method by measuring the Bragg reflected K-fluorescence signal of an iodine solution sample in a proof of principle experiment and to estimate the potential of the complete imaging setup using a Monte Carlo simulation, including a quantification of the minimal detectable tracer concentration for in vivo imaging. The proof of principle experiment shows that even for a small detector area of approximately 7 mm(2), the collimated and Bragg reflected K-fluorescence signal of a sample containing an iodine solution with a concentration of 50 mu g ml(-1) can be detected. The Monte Carlo simulation also shows that the proposed x-ray fluorescence imaging setup has the potential to image distributions of high-Z tracers in vivo at a radiation dose of a few mGy and at tracer concentrations down to 1 mu g ml(-1) for iodine in small animals. AU - Müller, B. AU - Hoeschen, C. AU - Grüner, F.* AU - Arkadiev, V.A.* AU - Johnson, T.R.C.* C1 - 28701 C2 - 33520 SP - 8063-8076 TI - Molecular imaging based on X-ray fluorescent high-Z tracers. JO - Phys. Med. Biol. VL - 58 IS - 22 PB - IOP Publishing PY - 2013 SN - 0031-9155 ER - TY - JOUR AB - Zebrafish has emerged as an excellent vertebrate model organism for studies of evolution, development and disease. Due to its external development and optical transparency in embryonic stages, zebrafish offers a major advantage over other vertebrate model organisms by being amenable for microscopic studies of biological processes within their natural environment directly in the living organism. However, commonly used zebrafish strains lose their transparency within their first two weeks of development and thus are no longer accessible for optical imaging approaches at juvenile or adult stages. In this study we successfully apply optoacoustic imaging for non-invasive three-dimensional imaging of adult zebrafish. Since optoacoustics does not necessarily require labeling, but can instead rely on the intrinsic tissue contrast, this imaging method has the potential to become a versatile tool for developmental studies from juvenile to adult stages in the intact zebrafish. AU - Ma, R. AU - Distel, M. AU - Dean-Ben, X.L. AU - Ntziachristos, V. AU - Razansky, D. C1 - 11376 C2 - 30646 SP - 7227-7237 TI - Non-invasive whole-body imaging of adult zebrafish with optoacoustic tomography. JO - Phys. Med. Biol. VL - 57 IS - 22 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - Intravascular near-infrared fluorescence (iNIRF) imaging can enable the in vivo visualization of biomarkers of vascular pathology, including high-risk plaques. The technique resolves the bio-distribution of systemically administered fluorescent probes with molecular specificity in the vessel wall. However, the geometrical variations that may occur in the distance between fibre-tip and vessel wall can lead to signal intensity variations and challenge quantification. Herein we examined whether the use of anatomical information of the cross-section vessel morphology, obtained from co-registered intravascular ultrasound (IVUS), can lead to quantification improvements when fibre-tip and vessel wall distance variations are present. The algorithm developed employs a photon propagation model derived from phantom experiments that is used to calculate the relative attenuation of fluorescence signals as they are collected over 360° along the vessel wall, and utilizes it to restore accurate fluorescence readings. The findings herein point to quantification improvements when employing hybrid iNIRF, with possible implications to the clinical detection of high-risk plaques or blood vessel theranostics. AU - Mallas, G.* AU - Brooks, D.H.* AU - Rosenthal, A. AU - Nudelman, R.N. AU - Mauskapf, A.* AU - Jaffer, F.A.* AU - Ntziachristos, V. C1 - 10685 C2 - 30327 SP - 6395-6406 TI - Improving quantification of intravascular fluorescence imaging using structural information. JO - Phys. Med. Biol. VL - 57 IS - 20 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - This paper presents effective and organ dose conversion coefficients for members of the public due to environmental external exposures, calculated using the ICRP adult male and female reference computational phantoms as well as voxel phantoms of a baby, two children and four adult individual phantoms--one male and three female, one of them pregnant. Dose conversion coefficients are given for source geometries representing environmental radiation exposures, i.e. whole body irradiations from a volume source in air, representing a radioactive cloud, a plane source in the ground at a depth of 0.5 g cm(-2), representing ground contamination by radioactive fall-out, and uniformly distributed natural sources in the ground. The organ dose conversion coefficients were calculated employing the Monte Carlo code EGSnrc simulating the photon transport in the voxel phantoms, and are given as effective and equivalent doses normalized to air kerma free-in-air at height 1 m above the ground in Sv Gy(-1). The findings showed that, in general, the smaller the body mass of the phantom, the higher the dose. The difference in effective dose between an adult and an infant is 80-90% at 50 keV and less than 40% above 100 keV. Furthermore, dose equivalent rates for photon exposures of several radionuclides for the above environmental exposures were calculated with the most recent nuclear decay data. Data are shown for effective dose, thyroid, colon and red bone marrow. The results are expected to facilitate regulation of exposure to radiation, relating activities of radionuclides distributed in air and ground to dose of the public due to external radiation as well as the investigation of the radiological effects of major radiation accidents such as the recent one in Fukushima and the decision making of several committees. AU - Petoussi-Henß, N. AU - Schlattl, H. AU - Zankl, M. AU - Endo, A.* AU - Saito, K.* C1 - 8594 C2 - 30198 SP - 5679-5713 TI - Organ doses from environmental exposures calculated using voxel phantoms of adults and children. JO - Phys. Med. Biol. VL - 57 IS - 18 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - A common dose-saving technique used in modern CT devices is automatic tube current modulation (TCM), which was originally designed to also reduce the dose in paediatric CT patients. In order to be able to deduce detailed organ doses of paediatric models, dose conversion coefficients normalized to CTDI(vol) for an eight-week-old baby and seven- and eight-year-old children have been computed accounting for TCM. The relative difference in organ dose conversion coefficients with and without TCM is for many organs and examinations less than 10%, but can in some cases amount up to 30%, e.g., for the thyroid in the chest CT of the seven-year-old child. Overall, the impact of TCM on the conversion coefficients increases with increasing age. Besides TCM, also the effect of collimation and tube voltage on organ dose conversion coefficients has been investigated. It could be shown that the normalization to CTDI(vol) leads to conversion coefficients that can in most cases be considered to be independent of collimation and tube voltage. AU - Schlattl, H. AU - Zankl, M. AU - Becker, J. AU - Hoeschen, C. C1 - 10518 C2 - 30312 SP - 6309-6326 TI - Dose conversion coefficients for paediatric CT examinations with automatic tube current modulation. JO - Phys. Med. Biol. VL - 57 IS - 20 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - This study shows that enhanced radiobiological effectiveness (RBE) values can be generated focusing low linear energy transfer (LET) radiation and thus changing the microdose distribution. 20 MeV protons (LET = 2.65 keV µm(-1)) are focused to submicrometer diameter at the ion microprobe superconducting nanoprobe for applied nuclear (Kern) physics experiments of the Munich tandem accelerator. The RBE values, as determined by measuring micronuclei (RBE(MN) = 1.48 ± 0.07) and dicentrics (RBE(D) = 1.92 ± 0.15), in human-hamster hybrid (A(L)) cells are significantly higher when 117 protons were focused to a submicrometer irradiation field within a 5.4 × 5.4 µm(2) matrix compared to quasi homogeneous in a 1 × 1 µm(2) matrix applied protons (RBE(MN) = 1.28 ± 0.07; RBE(D) = 1.41 ± 0.14) at the same average dose of 1.7 Gy. The RBE values are normalized to standard 70 kV (dicentrics) or 200 kV (micronuclei) x-ray irradiation. The 117 protons applied per point deposit the same amount of energy like a (12)C ion with 55 MeV total energy (4.48 MeV u(-1)). The enhancements are about half of that obtained for (12)C ions (RBE(MN) = 2.20 ± 0.06 and RBE(D) = 3.21 ± 0.10) and they are attributed to intertrack interactions of the induced damages. The measured RBE values show differences from predictions of the local effect model (LEM III) that is used to calculate RBE values for irradiation plans to treat tumors with high LET particles. AU - Schmid, T.E.* AU - Greubel, C.* AU - Hable, V.* AU - Zlobinskaya, O.* AU - Michalski, D.* AU - Girst, S.* AU - Siebenwirth, C.* AU - Schmid, E.* AU - Molls, M.* AU - Multhoff, G. AU - Dollinger, G.* C1 - 8603 C2 - 30201 SP - 5889-5907 TI - Low LET protons focused to submicrometer shows enhanced radiobiological effectiveness. JO - Phys. Med. Biol. VL - 57 IS - 19 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - The calculation of radiation dose from internally incorporated radionuclides is based on so-called absorbed fractions (AFs) and specific absorbed fractions (SAFs). SAFs for monoenergetic electrons were calculated for 63 source regions and 67 target regions using the new male and female adult reference computational phantoms adopted by the ICRP and ICRU and the Monte Carlo radiation transport programme package EGSnrc. The SAF values for electrons are opposed to the simplifying assumptions of ICRP Publication 30. The previously applied assumption of electrons being fully absorbed in the source organ itself is not always true at electron energies above approximately 300-500 keV. High-energy electrons have the ability to leave the source organ and, consequently, the electron SAFs for neighbouring organs can reach the same magnitude as those for photons for electron energies above 1 MeV. The reciprocity principle known for photons can be extended to electron SAFs as well, thus making cross-fire electron SAFs mass-independent. To quantify the impact of the improved electron dosimetry in comparison to the dosimetry using the simple assumptions of ICRP Publication 30, absorbed doses per administered activity of three radiopharmaceuticals were evaluated with and without explicit electron transport. The organ absorbed doses per administered activity for the two evaluation methods agree within 2%-3% for most organs for radionuclides with decay spectra having electron energies below a few hundred keV and within approximately 20% if higher electron energies are involved. An important exception is the urinary bladder wall, where the dose is overestimated by 60-150% using the simplified ICRP 30 approach for the radiopharmaceuticals of this study. AU - Zankl, M. AU - Schlattl, H. AU - Petoussi-Henß, N. AU - Hoeschen, C. C1 - 8232 C2 - 30948 SP - 4501-4526 TI - Electron specific absorbed fractions for the adult male and female ICRP/ICRU reference computational phantoms. JO - Phys. Med. Biol. VL - 57 IS - 14 PB - IOP Publishing PY - 2012 SN - 0031-9155 ER - TY - JOUR AB - In this paper, it is demonstrated that the effects of acoustic attenuation may play a significant role in establishing the quality of tomographic optoacoustic reconstructions. Accordingly, spatially dependent reduction of signal amplitude leads to quantification errors in the reconstructed distribution of the optical absorption coefficient while signal broadening causes loss of image resolution. Here we propose a correction algorithm for accounting for attenuation effects, which is applicable in both the time and frequency domains. It is further investigated which part of the optoacoustic signal spectrum is practically affected by those effects in realistic imaging scenarios. The validity and benefits of the suggested modelling and correction approaches are experimentally validated in phantom measurements. AU - Dean-Ben, X.L. AU - Razansky, D. AU - Ntziachristos, V. C1 - 6515 C2 - 28839 SP - 6129-6148 TI - The effects of acoustic attenuation in optoacoustic signals. JO - Phys. Med. Biol. VL - 56 IS - 18 PB - IOP Publishing PY - 2011 SN - 0031-9155 ER - TY - JOUR AB - X-ray radiation plays an important role in medical procedures ranging from diagnostics to therapeutics. Due to the harm such ionizing radiation can cause, it has become common practice to closely monitor the dosages received by patients. To this end, precise online dosimeters have been developed with the dual objectives of monitoring radiation in the region of interest and improving therapeutic methods. In this work, we evaluate GaN thin film high electron mobility heterostructures with sub-mm(2) detection areas as x-ray radiation detectors. Devices were tested using 40-300 kV Bremsstrahlung x-ray sources. We find that the photoconductive device response exhibits a large gain, is almost independent of the angle of irradiation, and is constant to within 2% of the signal throughout this medical diagnostic x-ray range, indicating that these sensors do not require recalibration for geometry or energy. Furthermore, the devices show a high sensitivity to x-ray intensity and can measure in the air kerma rate (free-in-air) range of 1 µGy s(-1) to 10 mGy s(-1) with a signal stability of ±1% and a linear total dose response over time. Medical conditions were simulated by measurements of device responses to irradiation through human torso phantoms. Direct x-ray imaging is demonstrated using the index finger and wrist sections of a human phantom. The results presented here indicate that GaN-based thin film devices exhibit a wide range of properties, which make them promising candidates for dosimetry applications. In addition, with potential detection volumes smaller than 10(-6) cm(3), they are well suited for high-resolution x-ray imaging. Moreover, with additional engineering steps, these devices can be adapted to potentially provide both in vivo biosensing and x-ray dosimetry. AU - Hofstetter, M. AU - Howgate, J.* AU - Sharp, I.D.* AU - Stutzmann, M.* AU - Thalhammer, S. C1 - 6414 C2 - 28631 SP - 3215-3231 TI - Development and evaluation of gallium nitride-based thin films for X-ray dosimetry. JO - Phys. Med. Biol. VL - 56 IS - 11 PB - IOP Publishing Ltd PY - 2011 SN - 0031-9155 ER - TY - JOUR AB - Near-field radiofrequency thermoacoustic (NRT) tomography is a new imaging method that was developed to mitigate limitations of conventional thermoacoustic imaging approaches, related to hard compromises between signal strength and spatial resolution. By utilizing ultrahigh-energy electromagnetic impulses at ∼20 ns duration along with improved energy absorption coupling in the near-field, this method can deliver high-resolution images without compromising signal to noise ratio. NRT is a promising modality, offering cost-effectiveness and ease of implementation and it can be conveniently scaled to image small animals and humans. However, several of the performance metrics of the method are not yet documented. In this paper, we characterize the expected imaging performance via numerical simulations based on a finite-integration time-domain (FITD) technique and experiments using tissue mimicking phantoms and different biological samples. Furthermore, we show for the first time whole-body tomographic imaging results from mice, revealing clear anatomical details along with highly dissipative inclusions introduced for control. The best spatial resolution achieved for those experiments was 150 µm. AU - Kellnberger, S. AU - Hajiaboli, A. AU - Razansky, D. AU - Ntziachristos, V. C1 - 3963 C2 - 28558 SP - 3433-3444 TI - Near-field thermoacoustic tomography of small animals. JO - Phys. Med. Biol. VL - 56 IS - 11 PB - IOP Publishing Ltd PY - 2011 SN - 0031-9155 ER - TY - JOUR AB - The radiation-induced posterior subcapsular cataract has long been generally accepted to be a deterministic effect that does not occur at doses below a threshold of at least 2 Gy. Recent epidemiological studies indicate that the threshold for cataract induction may be much lower or that there may be no threshold at all. A thorough study of this subject requires more accurate dose estimates for the eye lens than those available in ICRP Publication 74. Eye lens absorbed dose per unit fluence conversion coefficients for electron irradiation were calculated using a geometrical model of the eye that takes into account different cell populations of the lens epithelium, together with the MCNPX Monte Carlo radiation transport code package. For the cell population most sensitive to ionizing radiation-the germinative cells-absorbed dose per unit fluence conversion coefficients were determined that are up to a factor of 4.8 higher than the mean eye lens absorbed dose conversion coefficients for electron energies below 2 MeV. Comparison of the results with previously published values for a slightly different eye model showed generally good agreement for all electron energies. Finally, the influence of individual anatomical variability was quantified by positioning the lens at various depths below the cornea. A depth difference of 2 mm between the shallowest and the deepest location of the germinative zone can lead to a difference between the resulting absorbed doses of up to nearly a factor of 5000 for electron energy of 0.7 MeV. AU - Nogueira, P. AU - Zankl, M. AU - Schlattl, H. AU - Vaz, P.* C1 - 6114 C2 - 29001 CY - Bristol, UK SP - 6919-6934 TI - Dose conversion coefficients for monoenergetic electrons incident on a realistic human eye model with different lens cell populations. JO - Phys. Med. Biol. VL - 56 IS - 21 PB - IOP Publishing PY - 2011 SN - 0031-9155 ER - TY - JOUR AB - The emission of radiation from a contaminated body region is connected with the dose received by radiosensitive tissue through the specific absorbed fractions (SAFs) of emitted energy, which is therefore an essential quantity for internal dose assessment. A set of SAFs were calculated using the new adult reference computational phantoms, released by the International Commission on Radiological Protection (ICRP) together with the International Commission on Radiation Units and Measurements (ICRU). Part of these results has been recently published in ICRP Publication 110 (2009 Adult reference computational phantoms (Oxford: Elsevier)). In this paper, we mainly discuss the results and also present them in numeric form. The emission of monoenergetic photons and electrons with energies ranging from 10 keV to 10 MeV was simulated for three source organs: lungs, thyroid and liver. SAFs were calculated for four target regions in the body: lungs, colon wall, breasts and stomach wall. For quality assurance purposes, the simulations were performed simultaneously at the Helmholtz Zentrum München (HMGU, Germany) and at the Institute for Radiological Protection and Nuclear Safety (IRSN, France), using the Monte Carlo transport codes EGSnrc and MCNPX, respectively. The comparison of results shows overall agreement for photons and high-energy electrons with differences lower than 8%. Nevertheless, significant differences were found for electrons at lower energy for distant source/target organ pairs. Finally, the results for photons were compared to the SAF values derived using mathematical phantoms. Significant variations that can amount to 200% were found. The main reason for these differences is the change of geometry in the more realistic voxel body models. For electrons, no SAFs have been computed with the mathematical phantoms; instead, approximate formulae have been used by both the Medical Internal Radiation Dose committee (MIRD) and the ICRP due to the limitations imposed by the computing power available at this time. These approximations are mainly based on the assumption that electrons are absorbed locally in the source organ itself. When electron SAFs are calculated explicitly, discrepancies with this simplifying assumption are notable, especially at high energies and for neighboring organs where the differences can reach the same order of magnitude as for photon SAFs. AU - Hadid, L.* AU - Desbrée, A.* AU - Schlattl, H. AU - Franck, D.* AU - Blanchardon, E.* AU - Zankl, M. C1 - 3216 C2 - 27277 SP - 3631-3641 TI - Application of the ICRP/ICRU reference computational phantoms to internal dosimetry: Calculation of specific absorbed fractions of energy for photons and electrons. JO - Phys. Med. Biol. VL - 55 IS - 13 PB - IOP Publishing Ltd. PY - 2010 SN - 0031-9155 ER - TY - JOUR AB - Automatic tube current modulation (TCM) is used in modern CT devices. This is implemented in the numerical calculation of dose conversion coefficients for CT examinations. For four models of adults, the female and male reference models of ICRP and ICRU and a lighter and a heavier female model, dose conversion coefficients normalized to CTDI(vol) (DCC(CT)) have been computed with a Monte Carlo transport code for CT scans with and without TCM. It could be shown for both cases that reliable values for spiral CT scans are obtained when combining the results from an appropriate set of axial scans. The largest organ DCC(CT) are presented for typical CT examinations for all four models. The impact of TCM is greatest for chest, pelvis and whole-trunk CT examinations, where with TCM the effective DCC(CT) can be 20-25% lower than without TCM. Typical organs with strong dependence on TCM are thyroid, urinary bladder, lungs and oesophagus. While the DCC(CT) of thyroid and urinary bladder are mainly sensitive to angular TCM, the DCC(CT) of lungs and oesophagus are influenced primarily by longitudinal TCM. The impact of the body stature on the effective DCC(CT) is of the same order as the effect of TCM. Thus, for CT scans in the trunk region, accurate dose values can only be obtained when different sets of DCC(CT) are employed that are appropriate for the patient's sex and stature and the actual TCM settings. AU - Schlattl, H. AU - Zankl, M. AU - Becker, J. AU - Hoeschen, C. C1 - 5151 C2 - 27512 SP - 6243-6261 TI - Dose conversion coefficients for CT examinations of adults with automatic tube current modulation. JO - Phys. Med. Biol. VL - 55 IS - 20 PB - Institute of Physics and Engineering in Medicine PY - 2010 SN - 0031-9155 ER - TY - JOUR AB - Scatter correction is an open problem in x-ray cone beam (CB) CT. The measurement of scatter intensity with a moving beam stop array (BSA) is a promising technique that offers a low patient dose and accurate scatter measurement. However, when restoring the blocked primary fluence behind the BSA, spatial interpolation cannot well restore the high-frequency part, causing streaks in the reconstructed image. To address this problem, we deduce a projection correlation (PC) to utilize the redundancy (over-determined information) in neighbouring CB views. PC indicates that the main high-frequency information is contained in neighbouring angular projections, instead of the current projection itself, which provides a guiding principle that applies to high-frequency information restoration. On this basis, we present the projection correlation based view interpolation (PC-VI) algorithm; that it outperforms the use of only spatial interpolation is validated. The PC-VI based moving BSA method is developed. In this method, PC-VI is employed instead of spatial interpolation, and new moving modes are designed, which greatly improve the performance of the moving BSA method in terms of reliability and practicability. Evaluation is made on a high-resolution voxel-based human phantom realistically including the entire procedure of scatter measurement with a moving BSA, which is simulated by analytical ray-tracing plus Monte Carlo simulation with EGSnrc. With the proposed method, we get visually artefact-free images approaching the ideal correction. Compared with the spatial interpolation based method, the relative mean square error is reduced by a factor of 6.05-15.94 for different slices. PC-VI does well in CB redundancy mining; therefore, it has further potential in CBCT studies. AU - Yan, H.* AU - Mou, X.Q.* AU - Tang, S.J.* AU - Xu, Q.O.* AU - Zankl, M. C1 - 5995 C2 - 27794 CY - Bristol SP - 6353-6375 TI - Projection correlation based view interpolation for cone beam CT: Primary fluence restoration in scatter measurement with a moving beam stop array. JO - Phys. Med. Biol. VL - 55 IS - 21 PB - IOP Publishing Ltd PY - 2010 SN - 0031-9155 ER - TY - JOUR AB - Recent epidemiological studies suggest a rather low dose threshold (below 0.5 Gy) for the induction of a cataract of the eye lens. Some other studies even assume that there is no threshold at all. Therefore, protection measures have to be optimized and current dose limits for the eye lens may be reduced in the future. Two questions arise from this situation: first, which dose quantity is related to the risk of developing a cataract, and second, which personal dose equivalent quantity is appropriate for monitoring this dose quantity. While the dose equivalent quantity H-p(0.07) has often been seen as being sufficiently accurate for monitoring the dose to the lens of the eye, this would be questionable in the case when the dose limits were reduced and, thus, it may be necessary to generally use the dose equivalent quantity H-p(3) for this purpose. The basis for a decision, however, must be the knowledge of accurate conversion coefficients from fluence to equivalent dose to the lens. This is especially important for low-penetrating radiation, for example, electrons. Formerly published values of conversion coefficients are based on quite simple models of the eye. In this paper, quite a sophisticated model of the eye including the inner structure of the lens was used for the calculations and precise conversion coefficients for electrons with energies between 0.2 MeV and 12 MeV, and for angles of radiation incidence between 0 degrees and 45 degrees are presented. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are up to 1000 times smaller for electron energies below 1 MeV, nearly equal at 1 MeV and above 4 MeV, and by a factor of 1.5 larger at about 1.5 MeV electron energy. AU - Behrens, R.* AU - Dietze, G.* AU - Zankl, M. C1 - 1348 C2 - 26167 SP - 4069-4087 TI - Dose conversion coefficients for electron exposure of the human eye lens. JO - Phys. Med. Biol. VL - 54 IS - 13 PB - Iop Publishing Ltd PY - 2009 SN - 0031-9155 ER - TY - JOUR AB - The aim of this study was to investigate and quantify two biomarkers for radiation exposure (dicentrics and gamma-H2AX foci) in human lymphocytes after CT scans in the presence of an iodinated contrast agent. Blood samples from a healthy donor were exposed to CT scans in the absence or presence of iotrolan 300 at iodine concentrations of 5 or 50 mg ml(-1) blood. The samples were exposed to 0.025, 0.05, 0.1 and 1 Gy in a tissue equivalent body phantom. Chromosome aberration scoring and automated microscopic analysis of gamma-H2AX foci were performed in parts of the same samples. The theoretical physical dose enhancement factor (DEF) was calculated on the basis of the mass energy-absorption coefficients of iodine and blood and the photon energy spectrum of the CT tube. No significant differences in the yields of dicentrics and gamma-H2AX foci were observed in the absence or presence of 5 mg iodine ml(-1) blood up to 0.1 Gy, whereas at 1 Gy the yields were elevated for both biomarkers. At an iodine concentration of 50 mg ml(-1) serving as a positive control, a biological DEF of 9.5 +/- 1.4 and 2.3 +/- 0.5 was determined for dicentrics and gamma-H2AX foci, respectively. A physical DEF of 1.56 and 6.30 was calculated for 5 and 50 mg iodine ml(-1), respectively. Thus, it can be concluded that in the diagnostic dose range (radiation and contrast dose), no relevant biological dose-enhancing effect could be detected, whereas a clear biological dose-enhancing effect could be found for a contrast dose well outside the diagnostic CT range for the complete radiation dose range with both methods. AU - Jost, G.* AU - Golfier, S.* AU - Pietsch, H.* AU - Lengsfeld, P.* AU - Voth, M.* AU - Schmid, T.E.* AU - Eckardt-Schupp, F. AU - Schmid, E.* C1 - 1017 C2 - 27118 SP - 6029-6039 TI - The influence of x-ray contrast agents in computed tomography on the induction of dicentrics and γ-H2AX foci in lymphocytes of human blood samples. JO - Phys. Med. Biol. VL - 54 IS - 20 PB - IOP Publishing Ltd. PY - 2009 SN - 0031-9155 ER - TY - JOUR AB - Mesoscopic-scale living organisms (i.e. 1 mm to 1 cm sized) remain largely inaccessible by current optical imaging methods due to intensive light scattering in tissues. Therefore, imaging of many important model organisms, such as insects, fishes, worms and similarly sized biological specimens, is currently limited to embryonic or other transparent stages of development. This makes it difficult to relate embryonic cellular and molecular mechanisms to consequences in organ function and animal behavior in more advanced stages and adults. Herein, we have developed a selective-plane illumination optoacoustic tomography technique for in vivo imaging of optically diffusive organisms and tissues. The method is capable of whole-body imaging at depths from the sub-millimeter up to centimeter range with a scalable spatial resolution in the order of magnitude of a few tenths of microns. In contrast to pure optical methods, the spatial resolution here is not determined nor limited by light diffusion; therefore, such performance cannot be achieved by any other optical imaging technology developed so far. The utility of the method is demonstrated on several whole-body models and small-animal extremities. AU - Razansky, D. AU - Vinegoni, C.* AU - Ntziachristos, V. C1 - 1539 C2 - 26203 SP - 2769-2777 TI - Imaging of mesoscopic-scale organisms using selective-plane optoacoustic tomography. JO - Phys. Med. Biol. VL - 54 IS - 9 PB - Iop Publishing Ltd PY - 2009 SN - 0031-9155 ER - TY - JOUR AB - The fluence to organ-dose and effective-dose conversion coefficients for neutrons and protons with energies up to 100 GeV was calculated using the PHITS code coupled to male and female adult reference computational phantoms, which are to be released as a common ICRP/ICRU publication. For the calculation, the radiation and tissue weighting factors, w(R) and w(T), respectively, as revised in ICRP Publication 103 were employed. The conversion coefficients for effective dose equivalents derived using the radiation quality factors of both Q(L) andQ(y) relationships were also estimated, utilizing the functions for calculating the probability densities of the absorbed dose in terms of LET (L) and lineal energy (y), respectively, implemented in PHITS. By comparing these data with the corresponding data for the effective dose, we found that the numerical compatibilities of the revised wR with the Q(L) and Q(y) relationships are fairly established. The calculated data of these dose conversion coefficients are indispensable for constructing the radiation protection systems based on the new recommendations given in ICRP103 for aircrews and astronauts, as well as for workers in accelerators and nuclear facilities. AU - Sato, T.* AU - Endo, A.* AU - Zankl, M. AU - Petoussi-Henß, N. AU - Niita, K.* C1 - 1231 C2 - 26093 SP - 1997-2014 TI - Fluence-to-dose conversion coefficients for neutrons and protons calculated using the PHITS code and ICRP/ICRU adult reference computational phantoms. JO - Phys. Med. Biol. VL - 54 IS - 7 PB - Iop Publishing PY - 2009 SN - 0031-9155 ER - TY - JOUR AB - This note describes a new software tool called 'VolumeChange' that was developed to modify the masses and location of organs of virtual human voxel models. A voxel model is a three-dimensional representation of the human body in the form of an array of identification numbers that are arranged in slices, rows and columns. Each entry in this array represents a voxel; organs are represented by those voxels having the same identification number. With this tool, two human voxel models were adjusted to fit the reference organ masses of a male and a female adult, as defined by the International Commission on Radiological Protection (ICRP). The alteration of an already existing voxel model is a complicated process, leading to many problems that have to be solved. To solve those intricacies in an easy way, a new software tool was developed and is presented here. If the organs are modified, no bit of tissue, i.e. voxel, may vanish nor should an extra one appear. That means that organs cannot be modified without considering the neighbouring tissue. Thus, the principle of organ modification is based on the reassignment of voxels from one organ/tissue to another; actually deleting and adding voxels is only possible at the external surface, i.e. skin. In the software tool described here, the modifications are done by semi-automatic routines but including human control. Because of the complexity of the matter, a skilled person has to validate that the applied changes to organs are anatomically reasonable. A graphical user interface was designed to fulfil the purpose of a comfortable working process, and an adequate graphical display of the modified voxel model was developed. Single organs, organ complexes and even whole limbs can be edited with respect to volume, shape and location. AU - Becker, J. AU - Zankl, M. AU - Petoussi-Henß, N. C1 - 4406 C2 - 24408 SP - 195-205 TI - A software tool for modification of human voxel models used for application in radiation protection. JO - Phys. Med. Biol. VL - 52 PB - IOP Publ. PY - 2007 SN - 0031-9155 ER - TY - JOUR AB - The purpose of this work is to examine the effects of patient size on radiation dose from CT scans. To perform these investigations, we used Monte Carlo simulation methods with detailed models of both patients and multidetector computed tomography (MDCT) scanners. A family of three-dimensional, voxelized patient models previously developed and validated by the GSF was implemented as input files using the Monte Carlo code MCNPX. These patient models represent a range of patient sizes and ages (8 weeks to 48 years) and have all radiosensitive organs previously identified and segmented, allowing the estimation of dose to any individual organ and calculation of patient effective dose. To estimate radiation dose, every voxel in each patient model was assigned both a specific organ index number and an elemental composition and mass density. Simulated CT scans of each voxelized patient model were performed using a previously developed MDCT source model that includes scanner specific spectra, including bowtie filter, scanner geometry and helical source path. The scan simulations in this work include a whole-body scan protocol and a thoracic CT scan protocol, each performed with fixed tube current. The whole-body scan simulation yielded a predictable decrease in effective dose as a function of increasing patient weight. Results from analysis of individual organs demonstrated similar trends, but with some individual variations. A comparison with a conventional dose estimation method using the ImPACT spreadsheet yielded an effective dose of 0.14 mSv mAs(-1) for the whole-body scan. This result is lower than the simulations on the voxelized model designated 'Irene' (0.15 mSv mAs(-1)) and higher than the models 'Donna' and 'Golem' (0.12 mSv mAs(-1)). For the thoracic scan protocol, the ImPACT spreadsheet estimates an effective dose of 0.037 mSv mAs(-1), which falls between the calculated values for Irene (0.042 mSv mAs(-1)) and Donna (0.031 mSv mAs(-1)) and is higher relative to Golem (0.025 mSv mAs(-1)). This work demonstrates the ability to estimate both individual organ and effective doses from any arbitrary CT scan protocol on individual patient-based models and to provide estimates of the effect of patient size on these dose metrics. AU - DeMarco, J.J.* AU - Cagnon, C.H.* AU - Cody, D.D.* AU - Stevens, D.M.* AU - McCollough, C.H.* AU - Zankl, M. AU - Angel, E.* AU - McNitt-Gray, M.F.* C1 - 4358 C2 - 24335 SP - 2583-2597 TI - Estimating radiation doses from multidetector CT using Monte Carlo simulations: Effects of different size voxelized patient models on magnitudes of organ and effective dose. JO - Phys. Med. Biol. VL - 52 IS - 9 PB - IOP Publ. PY - 2007 SN - 0031-9155 ER - TY - JOUR AB - New organ dose conversion coefficients for coronary angiographic interventions are presented, as well as dose distributions and resulting maximal local dose conversion coefficients in the relevant organs. For the Monte Carlo based simulations, voxel models of the human anatomy were employed which represent the average Caucasian adult man and woman as defined by the International Commission on Radiological Protection. In the 21 investigated projections, the mean organ dose conversion coefficients vary from a few 0.01 to 2 mGy(Gy cm2)-1, depending on the projections. However, especially in portions of the lungs and the active bone marrow, the conversion coefficients can locally amount up to 10 mGy(Gy cm2)-1, which is half the average conversion coefficient of the skin at the field entrance. In addition to the dose conversion coefficients, the dependence of the patient dose on the projection has been estimated. It could be shown that the patient doses are highest for left anterior oblique views with strong caudal or cranial orientation. Nevertheless, for a large range of image-intensifier positions no significant dose differences could be found. AU - Schlattl, H. AU - Zankl, M. AU - Hausleiter, J.* AU - Hoeschen, C. C1 - 169 C2 - 24528 SP - 4393-4408 TI - Local organ dose conversion coefficients for angiographic examinations of coronary arteries. JO - Phys. Med. Biol. VL - 52 IS - 15 PB - IOP Publ. PY - 2007 SN - 0031-9155 ER - TY - JOUR AB - A new series of organ equivalent dose conversion coefficients for whole body external photon exposure is presented for a standardized couple of human voxel models, called Rex and Regina. Irradiations from broad parallel beams in antero-posterior, postero-anterior, left- and right-side lateral directions as well as from a 360° rotational source have been performed numerically by the Monte Carlo transport code EGSnrc. Dose conversion coefficients from an isotropically distributed source were computed, too. The voxel models Rex and Regina originating from real patient CT data comply in body and organ dimensions with the currently valid reference values given by the International Commission on Radiological Protection (ICRP) for the average Caucasian man and woman, respectively. While the equivalent dose conversion coefficients of many organs are in quite good agreement with the reference values of ICRP Publication 74, for some organs and certain geometries the discrepancies amount to 30% or more. Differences between the sexes are of the same order with mostly higher dose conversion coefficients in the smaller female model. However, much smaller deviations from the ICRP values are observed for the resulting effective dose conversion coefficients. With the still valid definition for the effective dose (ICRP Publication 60), the greatest change appears in lateral exposures with a decrease in the new models of at most 9%. However, when the modified definition of the effective dose as suggested by an ICRP draft is applied, the largest deviation from the current reference values is obtained in postero-anterior geometry with a reduction of the effective dose conversion coefficient by at most 12%. AU - Schlattl, H. AU - Zankl, M. AU - Petoussi-Henß, N. C1 - 5813 C2 - 24423 SP - 2123-2145 TI - Organ dose conversion coefficients for voxel models of the reference male and female from idealized photon exposures. JO - Phys. Med. Biol. VL - 52 IS - 8 PB - IOP Publ. PY - 2007 SN - 0031-9155 ER - TY - JOUR AU - Treiber, O. AU - Wanninger, F. AU - Führ, H. AU - Panzer, W. AU - Regulla, D.F. AU - Winkler, G. C1 - 9946 C2 - 20949 SP - 449-466 TI - An adaptive algorithm for the detection of microcalcifications in simulated low-dose mammography. JO - Phys. Med. Biol. VL - 48 PY - 2003 SN - 0031-9155 ER - TY - JOUR AB - Voxel phantoms are human models based on computed tomographic or magnetic resonance images obtained from high-resolution scans of a single individual. They consist of a huge number of volume elements (voxels) and are at the moment the most precise representation of the human anatomy. The purpose of this paper is to introduce the GSF voxel phantoms, with emphasis on the new ones and highlight their characteristics and limitations. The GSF voxel family includes at the moment two paediatric and five adult phantoms of both sexes, different ages and stature and several others are under construction. Two phantoms made of physical calibration phantoms are also available to be used for validation purposes. The GSF voxel phantoms tend to cover persons of individual anatomy, and were developed to be used for numerical dosimetry of radiation transport but other applications are also possible. Examples of applications in patient dosimetry in, diagnostic radiology and in nuclear medicine as well as for whole-body irradiations from idealized external exposures are given and discussed. AU - Petoussi-Henß, N. AU - Zankl, M. AU - Fill, U. AU - Regulla, D.F. C1 - 9947 C2 - 20184 SP - 89-106 TI - The GSF family of voxel phantoms. JO - Phys. Med. Biol. VL - 47 PB - IOP Publication PY - 2002 SN - 0031-9155 ER - TY - JOUR AB - New organ equivalent dose conversion coefficients are presented for whole body irradiation with monoenergetic photons of energies between 10 keV and 10 MeV for idealized geometries and seven adult male and female voxel models. The geometries are broad parallel photon beams in anterior-posterior, posterior-anterior, left-and right-lateral direction and a full 360degrees rotation around the body length axis. Dose differences between the different voxel models are below approximately 30% for some organs and geometries in the energy range between 60 and 200 keV, but they can be up to 100% or more in single cases, due to differences in stature and individual anatomical details. For low photon energies, the differences may amount to hundreds of per cent. Extensive comparisons of the dose conversion coefficients with respective values calculated using mathematical body models revealed various degrees of unrealistic positioning of single organs in the latter models. Examples are the kidneys, spleen and stomach that are located too superficially in the mathematical models. Over- or underestimations of several tens of per cent may, thus, occur for the mathematical models, compared to the voxel models considered. In contrast to previous assumptions, when the mathematical models have been used to establish reference organ dose conversion coefficients, it can be concluded that they do not properly represent a large population of individuals. AU - Zankl, M. AU - Fill, U. AU - Petoussi-Henß, N. AU - Regulla, D.F. C1 - 9948 C2 - 20264 SP - 2367-2385 TI - Organ dose conversion coefficients for external photon irradiation of male and female voxel models. JO - Phys. Med. Biol. VL - 47 PB - IOP Publication PY - 2002 SN - 0031-9155 ER - TY - JOUR AB - The objective of this study is to establish a comprehensive set of backscatter factors for mammography based on the exposure model proposed by the European Protocol on Dosimetry in Mammography. The Monte Carlo calculated backscatter factors (BSFs) presented in this study are for various exposure conditions encountered in mammographic practice as well as in calibration procedures. The data demonstrate the variation of the BSF as a function of the exposure parameters, hence enabling a better match with calibration conditions and, at the same time, reviewing the BSF data already recommended by the European Protocol. Furthermore, earlier data for BSF for general diagnostic radiology are validated. AU - Kramer, R.* AU - Drexler, G.* AU - Petoussi-Henß, N. AU - Zankl, M. AU - Regulla, D.F. AU - Panzer, W. C1 - 9945 C2 - 19839 SP - 771-781 TI - Backscatter factors for mammography calculated with Monte Carlo methods. JO - Phys. Med. Biol. VL - 46 IS - 3 PB - IOP Publishing Ltd. PY - 2001 SN - 0031-9155 ER - TY - JOUR AU - Stieve, F.-E. C1 - 19463 C2 - 12558 SP - 687-708 TI - Medical Physics, in the Past, today and in the Future - the Development of Medical Physics from the Point of View of a Radiologist. JO - Phys. Med. Biol. VL - 36 PY - 1991 SN - 0031-9155 ER - TY - JOUR AU - Stieve, F.E. C1 - 40838 C2 - 38026 SP - 687-708 TI - Medical physics, in the past, today and in the future - the development of medical physics from the point of view of a radiologist. JO - Phys. Med. Biol. VL - 36 IS - 6 PY - 1991 SN - 0031-9155 ER - TY - JOUR AU - Lipinski, H.-G. C1 - 18465 C2 - 11119 SP - 441-447 TI - Monte Carlo Simulation of Extracellular Diffusion in Brain Tissues. JO - Phys. Med. Biol. VL - 35 PY - 1990 SN - 0031-9155 ER - TY - JOUR AU - Lipinski, H.G. C1 - 41993 C2 - 40143 SP - 441-447 TI - Monte Carlo simulation of extracellular diffusion in brain tissues. JO - Phys. Med. Biol. VL - 35 IS - 3 PY - 1990 SN - 0031-9155 ER - TY - JOUR AB - A Monte Carlo technique has been employed to calculate the energy deposition events in small cylindrical targets (less than or equal to 100 nm), including sizes which represent the DNA duplex, nucleosome and chromatin fibre, by simulated electron tracks from C (278 eV), A1 (1487 eV) and Ti (4509 eV) characteristic ultrasoft x-rays in water. Detailed examples of input data tables for the generation of electron tracks produced from the x-ray photon interactions are presented. Frequencies of energy deposition events per gray for target sizes from 1 to 100 nm are given and comparisons have been made with radiations of different qualities. AU - Nikjoo, H. AU - Goodhead, D.T. AU - Charlton, D.E. AU - Paretzke, H.G. C1 - 18911 C2 - 11279 SP - 691-705 TI - Energy Deposition in Small Cylindrical Targets by Ultrasoft x-rays. JO - Phys. Med. Biol. VL - 34 IS - 6 PY - 1989 SN - 0031-9155 ER - TY - JOUR AU - Makarewicz, M. AU - Burger, G.T. C1 - 41555 C2 - 36090 SP - 1165 TI - Remark on recommendations of neutron dosimetry protocols. JO - Phys. Med. Biol. VL - 31 IS - 10 PY - 1986 SN - 0031-9155 ER - TY - JOUR AU - Makarewicz, M. AU - Burger, G.T. C1 - 41708 C2 - 38377 SP - 281-284 TI - On the stopping power for tissue-equivalent gaseous ionisation devices used in neutron dosimetry. JO - Phys. Med. Biol. VL - 31 IS - 3 PY - 1986 SN - 0031-9155 ER - TY - JOUR AB - With a view to the application of fast neutrons in medicine and biology the G-value for the standard (Fricke) ferrous sulphate solution was determined for 3 and 14 MeV neutrons by comparison with the ionometric method. Knowledge of the G-value enables us to use for dosimetry the chemical technique which is of advantage wherever the irradiated object does not have a simple geometry, as in the case in many biological and medical experiments. AU - Pejuan, A. AU - Kuehn, H. C1 - 33693 C2 - 38617 SP - 163-169 TI - The G-value of the ferrous sulphate dosemeter for 3 and 14 MeV neutrons. JO - Phys. Med. Biol. VL - 26 IS - 1 PY - 1981 SN - 0031-9155 ER - TY - JOUR AB - The direct result of a spectrometric measurement is a pulse height distribution. In the energy region up to 300 keV three corrections in particular need to be applied to get the photon spectrum: corrections for K-escape, Compton scattering and inefficient photon absorption. A simple 'stripping' procedures is described which may be implemented on a desk type computer. All data necessary are either available in the literature or may be derived from the measurement of very heavily filtered X-ray spectra. The accuracy of the procedure is better than ± 5% of the peak value. Results are compared with a more detailed stripping procedure, based on Monte Carlo calculated data. AU - Seelentag, W.W. AU - Panzer, W. C1 - 41825 C2 - 38166 SP - 767-780 TI - Stripping of X ray bremsstrahlung spectra up to 300 kVp on a desk type computer. JO - Phys. Med. Biol. VL - 24 IS - 4 PY - 1979 SN - 0031-9155 ER - TY - JOUR AB - A modified form of ferrous sulphate dosemeter is described, which retains the accepted advantages of the Fricke dosemeter and possesses the following additional properties: (a) it determines the dose in water; (b) the response is independent (to within +or-1.5%) of effective photon energy over the range 24 keV to 50 MeV and, therefore, independent of the shape of X-ray spectrum; (c) the low concentration of sulphuric acid reduces the possibility of introducing impurities from the source. AU - Frankenberg, D. C1 - 41977 C2 - 37955 SP - 597-605 TI - A ferrous sulphate dosemeter independent of photon energy in the range from 25 keV up to 50 MeV. JO - Phys. Med. Biol. VL - 14 IS - 4 PY - 1969 SN - 0031-9155 ER - TY - JOUR AB - Factors which can influence measurements of the practical range of fast electrons are stated and discussed. These factors can be divided into geometrical parameters, like beam divergence, diameter of the beam and diameter of the detector, and into factors which influence particle energy. It is concluded that the energy-range relations of Katz and Penfold in aluminium and of Markus in water can be used in the energy range from 10 to 30 Mev with a maximum uncertainty of about 2%. AU - Nüsse, M. C1 - 42003 C2 - 37959 SP - 315-321 TI - Factors affecting the energy-range relation of fast electrons in aluminium. JO - Phys. Med. Biol. VL - 14 IS - 2 PY - 1969 SN - 0031-9155 ER -