TY - JOUR AB - The last decade has seen a large growth in fluorescence-guided surgery (FGS) imaging and interventions. With the increasing number of clinical specialties implementing FGS, the range of systems with radically different physical designs, image processing approaches, and performance requirements is expanding. This variety of systems makes it nearly impossible to specify uniform performance goals, yet at the same time, utilization of different devices in new clinical procedures and trials indicates some need for common knowledge bases and a quality assessment paradigm to ensure that effective translation and use occurs. It is feasible to identify key fundamental image quality characteristics and corresponding objective test methods that should be determined such that there are consistent conventions across a variety of FGS devices. This report outlines test methods, tissue simulating phantoms and suggested guidelines, as well as personnel needs and professional knowledge bases that can be established. This report frames the issues with guidance and feedback from related societies and agencies having vested interest in the outcome, coming from an independent scientific group formed from academics and international federal agencies for the establishment of these professional guidelines. AU - Pogue, B.W.* AU - Zhu, T.C.* AU - Ntziachristos, V. AU - Wilson, B.C.* AU - Paulsen, K.D.* AU - Gioux, S.* AU - Nordstrom, R.J.* AU - Pfefer, T.J.* AU - Tromberg, B.J.* AU - Wabnitz, H.* AU - Yodh, A.G.* AU - Chen, Y.* AU - Litorja, M.* C1 - 68947 C2 - 53786 CY - 111 River St, Hoboken 07030-5774, Nj Usa TI - AAPM Task Group Report 311: Guidance for performance evaluation of fluorescence-guided surgery systems. JO - Med. Phys. PB - Wiley PY - 2023 SN - 0094-2405 ER - TY - JOUR AB - BACKGROUND: Microbeam and x-ray FLASH radiation therapy are innovative concepts that promise reduced normal tissue toxicity in radiation oncology without compromising tumor control. However, currently only large third-generation synchrotrons deliver acceptable x-ray beam qualities and there is a need for compact, hospital-based radiation sources to facilitate clinical translation of these novel treatment strategies. PURPOSE: We are currently setting up the first prototype of a line-focus x-ray tube (LFxT), a promising technology that may deliver ultra-high dose rates (UHDR) of more than 100Gy/s from a table-top source. The operation of the source in the heat capacity limit allows very high dose rates with micrometer-sized focal spot widths. Here, we investigate concepts of effective heat management for the LFxT, a prerequisite for the performance of the source. METHODS: For different focal spot widths, we investigated the temperature increase numerically with Monte Carlo simulations and finite element analysis (FEA). We benchmarked the temperature and thermal stresses at the focal spot against a commercial x-ray tube with similar power characteristics. We assessed thermal loads at the vacuum chamber housing caused by scattering electrons in Monte Carlo simulations and FEA. Further, we discuss active cooling strategies and present a design of the rotating target. RESULTS: Conventional focal spot widths led to a temperature increase dominated by heat conduction, while very narrow focal spots led to a temperature increase dominated by the heat capacity of the target material. Due to operation in the heat capacity limit, the temperature increase at the focal spot was lower than for the investigated commercial x-ray tube. Hence, the thermal stress at the focal spot of the LFxT was considered uncritical. The target shaft and the vacuum chamber housing require active cooling to withstand the high heat loads. CONCLUSIONS: The heat capacity limit allows very high power densities at the focal spot of the LFxT and thus facilitates very high dose rates. Numerical simulations demonstrated that the heat load imparted by scattering electrons requires active cooling. AU - Winter, J. AU - Dimroth, A.* AU - Roetzer, S.* AU - Zhang, Y.* AU - Krämer, K.L.* AU - Petrich, C. AU - Matejcek, C.* AU - Aulenbacher, K.* AU - Zimmermann, M.* AU - Combs, S.E. AU - Galek, M.* AU - Natour, G.* AU - Butzek, M.* AU - Wilkens, J.J.* AU - Bartzsch, S. C1 - 64619 C2 - 52347 TI - Heat management of a compact x-ray source for microbeam radiotherapy and FLASH treatments. JO - Med. Phys. VL - 49 IS - 5 PY - 2022 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: The size specific dose estimate (SSDE) is a metric that adjusts CTDIvol to account for patient size. While not intended to be an estimate of organ dose, AAPM Report 204 notes the difference between the patient organ dose and SSDE is expected to be 10-20%. The purpose of this work was therefore to evaluate SSDE against estimates of organ dose obtained using Monte Carlo (MC) simulation techniques applied to routine exams across a wide range of patient sizes. MATERIALS AND METHODS: SSDE was evaluated with respect to organ dose based for three routine protocols taken from Siemens scanners: (1) brain parenchyma dose in routine head exams; (2) lung and breast dose in routine chest exams; and (3) liver, kidney, and spleen dose in routine abdomen/pelvis exams. For each exam, voxelized phantom models were created from existing models or derived from clinical patient scans. For routine head exams, 15 patient models were used which consisted of 10 GSF/ICRP voxelized phantom models and 5 pediatric voxelized patient models created from CT image data. For all exams, the size metric used was water equivalent diameter (Dw ). For the routine chest exams, data from 161 patients were collected with a Dw range of ~16 to 44 cm. For the routine abdomen/pelvis exams, data from 107 patients were collected with a range of Dw from ~16 to 44 cm. Image data from these patients were segmented to generate voxelized patient models. For routine head exams, fixed tube current (FTC) was used while tube current modulation (TCM) data for body exams were extracted from raw projection data. The voxelized patient models and tube current information were used in detailed MC simulations for organ dose estimation. Organ doses from MC simulation were normalized by CTDIvol and parameterized as a function of Dw . For each patient scan, the SSDE was obtained using Dw and CTDIvol values of each scan, according to AAPM Report 220 for body scans and Report 293 for head scans. For each protocol and each patient, normalized organ doses were compared to SSDE. A one-sided tolerance limit covering 95% (p = 0.95) of the population with 95% confidence (α = 0.05) was used to assess the upper tolerance limit (TU ) between SSDE and normalized organ dose. RESULTS: For head exams, the TU between SSDE and brain parenchyma dose was observed to be 12.5%. For routine chest exams, the TU between SSDE and lung and breast dose was observed to be 35.6% and 68.3%, respectively. For routine abdomen/pelvis exams, the TU between SSDE and liver, spleen, and kidney dose was observed to be 30.7%, 33.2%, and 33.0%, respectively. CONCLUSIONS: The TU of 20% between SSDE and organ dose was found to be insufficient to cover 95% of the sampled population with 95% confidence for all of the organs and protocols investigated, except for brain parenchyma dose. For the routine body exams, excluding the breasts, a wider threshold difference of ~30-36% would be needed. These results are, however, specific to Siemens scanners. AU - Hardy, A.J.* AU - Bostani, M.* AU - Kim, G.H.J.* AU - Cagnon, C.H.* AU - Zankl, M. AU - McNitt-Gray, M.* C1 - 62629 C2 - 51011 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 6160-6173 TI - Evaluating size-specific dose estimate (SSDE) as an estimate of organ doses from routine CT exams derived from Monte Carlo simulations. JO - Med. Phys. VL - 48 IS - 10 PB - Wiley PY - 2021 SN - 0094-2405 ER - TY - JOUR AB - Purpose X-ray microbeam radiation therapy is a preclinical concept for tumor treatment promising tissue sparing and enhanced tumor control. With its spatially separated, periodic micrometer-sized pattern, this method requires a high dose rate and a collimated beam typically available at large synchrotron radiation facilities. To treat small animals with microbeams in a laboratory-sized environment, we developed a dedicated irradiation system at the Munich Compact Light Source (MuCLS). Methods A specially made beam collimation optic allows to increase x-ray fluence rate at the position of the target. Monte Carlo simulations and measurements were conducted for accurate microbeam dosimetry. The dose during irradiation is determined by a calibrated flux monitoring system. Moreover, a positioning system including mouse monitoring was built. Results We successfully commissioned thein vivomicrobeam irradiation system for an exemplary xenograft tumor model in the mouse ear. By beam collimation, a dose rate of up to 5.3 Gy/min at 25 keV was achieved. Microbeam irradiations using a tungsten collimator with 50 mu m slit size and 350 mu m center-to-center spacing were performed at a mean dose rate of 0.6 Gy/min showing a high peak-to-valley dose ratio of about 200 in the mouse ear. The maximum circular field size of 3.5 mm in diameter can be enlarged using field patching. Conclusions This study shows that we can performin vivomicrobeam experiments at the MuCLS with a dedicated dosimetry and positioning system to advance this promising radiation therapy method at commercially available compact microbeam sources. Peak doses of up to 100 Gy per treatment seem feasible considering a recent upgrade for higher photon flux. The system can be adapted for tumor treatment in different animal models, for example, in the hind leg. AU - Burger, K.* AU - Urban, T.* AU - Dombrowsky, A. AU - Dierolf, M.* AU - Günther, B.* AU - Bartzsch, S.* AU - Achterhold, K.* AU - Combs, S.E. AU - Schmid, T.E. AU - Wilkens, J.J.* AU - Pfeiffer, F.* C1 - 59877 C2 - 49084 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 5183-5193 TI - Technical and dosimetric realization ofin vivox-ray microbeam irradiations at the Munich Compact Light Source. JO - Med. Phys. VL - 47 IS - 10 PB - Wiley PY - 2020 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Current techniques and procedures for dosimetry in microbeams typically rely on radiochromic film or small volume ionization chambers for validation and quality assurance in 2D and 1D, respectively. Whilst well characterized for clinical and preclinical radiotherapy, these methods are noninstantaneous and do not provide real time profile information. The objective of this work is to determine the suitability of the newly developed vM1212 detector, a pixelated CMOS (complementary metal-oxide-semiconductor) imaging sensor, for in situ and in vivo verification of x-ray microbeams. Methods: Experiments were carried out on the vM1212 detector using a 220 kVp small animal radiation research platform (SARRP) at the Helmholtz Centre Munich. A 3 x 3 cm2 square piece of EBT3 film was placed on top of a marked nonfibrous card overlaying the sensitive silicon of the sensor. One centimemter of water equivalent bolus material was placed on top of the film for build-up. The response of the detector was compared to an Epson Expression 10000XL flatbed scanner using FilmQA Pro with triple channel dosimetry. This was also compared to a separate exposure using 450 µm of silicon as a surrogate for the detector and a Zeiss Axio Imager 2 microscope using an optical microscopy method of dosimetry. Microbeam collimator slits with range of nominal widths of 25, 50, 75, and 100 µm were used to compare beam profiles and determine sensitivity of the detector and both film measurements to different microbeams. Results: The detector was able to measure peak and valley profiles in real-time, a significant reduction from the 24 hr self-development required by the EBT3 film. Observed full width at half maximum (FWHM) values were larger than the nominal slit widths, ranging from 130 to 190 µm due to divergence. Agreement between the methods was found for peak-to-valley dose ratio (PVDR), peak to peak separation and FWHM, but a difference in relative intensity of the microbeams was observed between the detectors. Conclusions: The investigation demonstrated that pixelated CMOS sensors could be applied to microbeam radiotherapy for real-time dosimetry in the future, however the relatively large pixel pitch of the vM1212 detector limit the immediate application of the results. AU - Flynn, S.* AU - Price, T.* AU - Allport, P.* AU - Silvestre Patallo, I.* AU - Thomas, R.* AU - Subiel, A.* AU - Bartzsch, S. AU - Treibel, F.* AU - Ahmed, M.* AU - Jacobs-Headspith, J.* AU - Edwards, T.* AU - Jones, I.* AU - Cathie, D.* AU - Guerrini, N.* AU - Sedgwick, I.* C1 - 57637 C2 - 47918 CY - 111 River St, Hoboken 07030-5774, Nj Usa TI - Evaluation of a pixelated large format CMOS sensor for x-ray microbeam radiotherapy. JO - Med. Phys. PB - Wiley PY - 2019 SN - 0094-2405 ER - TY - JOUR AB - PurposeSize-specific dose estimates (SSDE) conversion factors have been determined by AAPM Report 204 to adjust CTDIvol to account for patient size but were limited to body CT examinations. The purpose of this work was to determine conversion factors that could be used for an SSDE for helical, head CT examinations for patients of different sizes.MethodsValidated Monte Carlo (MC) simulation methods were used to estimate dose to the center of the scan volume from a routine, helical head examination for a group of patient models representing a range of ages and sizes. Ten GSF/ICRP voxelized phantom models and five pediatric voxelized patient models created from CT image data were used in this study. CT scans were simulated using a Siemens multidetector row CT equivalent source model. Scan parameters were taken from the AAPM Routine Head protocols for a fixed tube current (FTC), helical protocol, and scan lengths were adapted to the anatomy of each patient model. MC simulations were performed using mesh tallies to produce voxelized dose distributions for the entire scan volume of each model. Three tally regions were investigated: (1) a small 0.6cc volume at the center of the scan volume, (2) 0.8-1.0cm axial slab at the center of the scan volume, and (3) the entire scan volume. Mean dose to brain parenchyma for all three regions was calculated. Mean bone dose and a mass-weighted average dose, consisting of brain parenchyma and bone, were also calculated for the slab in the central plane and the entire scan volume. All dose measures were then normalized by CTDIvol for the 16cm phantom (CTDIvol,16). Conversion factors were determined by calculating the relationship between normalized doses and water equivalent diameter (D-w).ResultsCTDI(vol,16)-normalized mean brain parenchyma dose values within the 0.6cc volume, 0.8-1.0cm central axial slab, and the entire scan volume, when parameterized by D-w, had an exponential relationship with a coefficient of determination (R-2) of 0.86, 0.84, and 0.88, respectively. There was no statistically significant difference between the conversion factors resulting from these three different tally regions. Exponential relationships between CTDIvol,16-normalized mean bone doses had R-2 values of 0.83 and 0.87 for the central slab and for the entire scan volume, respectively. CTDIvol,16-normalized mass-weighted average doses had R-2 values of 0.39 and 0.51 for the central slab and for the entire scan volume, respectively.ConclusionsConversion factors that describe the exponential relationship between CTDIvol,16-normalized mean brain dose and a size metric (D-w) for helical head CT examinations have been reported for two different interpretations of the center of the scan volume. These dose descriptors have been extended to describe the dose to bone in the center of the scan volume as well as a mass-weighted average dose to brain and bone. These may be used, when combined with other efforts, to develop an SSDE dose coefficients for routine, helical head CT examinations. AU - Hardy, A.J.* AU - Bostani, M.* AU - Hernandez, A.M.* AU - Zankl, M. AU - McCollough, C.H.* AU - Cagnon, C.H.* AU - Boone, J.M.* AU - McNitt-Gray, M.* C1 - 55006 C2 - 46040 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 902-912 TI - Estimating a size-specific dose for helical head CT examinations using Monte Carlo simulation methods. JO - Med. Phys. VL - 46 IS - 2 PB - Wiley PY - 2019 SN - 0094-2405 ER - TY - JOUR AB - Purpose Identification of morphological characteristics of skin lesions is of vital importance in diagnosing diseases with dermatological manifestations. This task is often performed manually or in an automated way based on intensity level. Recently, ultra-broadband raster-scan optoacoustic mesoscopy (UWB-RSOM) was developed to offer unique cross-sectional optical imaging of the skin. A machine learning (ML) approach is proposed here to enable, for the first time, automated identification of skin layers in UWB-RSOM data. Materials and methods The proposed method, termed SkinSeg, was applied to coronal UWB-RSOM images obtained from 12 human participants. SkinSeg is a multi-step methodology that integrates data processing and transformation, feature extraction, feature selection, and classification. Various image features and learning models were tested for their suitability at discriminating skin layers including traditional machine learning along with more advanced deep learning algorithms. An support vector machines-based postprocessing approach was finally applied to further improve the classification outputs. Results Random forest proved to be the most effective technique, achieving mean classification accuracy of 86.89% evaluated based on a repeated leave-one-out strategy. Insights about the features extracted and their effect on classification accuracy are provided. The highest accuracy was achieved using a small group of four features and remained at the same level or was even slightly decreased when more features were included. Convolutional neural networks provided also promising results at a level of approximately 85%. The application of the proposed postprocessing technique was proved to be effective in terms of both testing accuracy and three-dimensional visualization of classification maps. Conclusions SkinSeg demonstrated unique potential in identifying skin layers. The proposed method may facilitate clinical evaluation, monitoring, and diagnosis of diseases linked to skin inflammation, diabetes, and skin cancer. AU - Moustakidis, S.* AU - Omar, M. AU - Aguirre Bueno, J. AU - Mohajerani, P. AU - Ntziachristos, V. C1 - 56583 C2 - 47162 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 4046-4056 TI - Fully automated identification of skin morphology in raster-scan optoacoustic mesoscopy using artificial intelligence. JO - Med. Phys. VL - 46 IS - 9 PB - Wiley PY - 2019 SN - 0094-2405 ER - TY - JOUR AB - PurposeThe purpose of this study was to estimate the radiation dose to the lung and breast as well as the effective dose from tube current modulated (TCM) lung cancer screening (LCS) scans across a range of patient sizes.MethodsMonte Carlo (MC) methods were used to calculate lung, breast, and effective doses from a low-dose LCS protocol for a 64-slice CT that used TCM. Scanning parameters were from the protocols published by AAPM's Alliance for Quality CT. To determine lung, breast, and effective doses from lung cancer screening, eight GSF/ICRP voxelized phantom models with all radiosensitive organs identified were used to estimate lung, breast, and effective doses. Additionally, to extend the limited size range provided by the GSF/ICRP phantom models, 30 voxelized patient models of thoracic anatomy were generated from LCS patient data. For these patient models, lung and breast were semi-automatically segmented. TCM schemes for each of the GSF/ICRP phantom models were generated using a validated method wherein tissue attenuation and scanner limitations were used to determine the TCM output as a function of table position and source angle. TCM schemes for voxelized patient models were extracted from the raw projection data. The water equivalent diameter, Dw, was used as the patient size descriptor. Dw was estimated for the GSF/ICRP models. For the thoracic patient models, Dw was extracted from the DICOM header of the CT localizer radiograph. MC simulations were performed using the TCM scheme for each model. Absolute organ doses were tallied and effective doses were calculated using ICRP 103 tissue weighting factors for the GSF/ICRP models. Metrics of scanner radiation output were determined based on each model's TCM scheme, including CTDIvol, dose length product (DLP), and CTDIvol, Low Att, a previously described regional metric of scanner output covering most of the lungs and breast. All lung and breast doses values were normalized by scan-specific CTDIvol and CTDIvol, Low Att. Effective doses were normalized by scan-specific CTDIvol and DLP. Absolute and normalized doses were reported as a function of Dw.ResultsLung doses normalized by CTDIvol, Low Att were modeled as an exponential relationship with respect to Dw with coefficients of determination (R-2) of 0.80. Breast dose normalized by CTDIvol, Low Att was modeled with an exponential relationship to Dw with an R-2 of 0.23. For all eight GSF/ICRP phantom models, the effective dose using TCM protocols was below 1.6 mSv. Effective doses showed some size dependence but when normalized by DLP demonstrated a constant behavior.ConclusionLung, breast, and effective doses from LCS CT exams with TCM were estimated with respect to patient size. Normalized lung dose can be reasonably estimated with a measure of a patient size such as Dw and regional metric of CTDIvol covering the thorax such as CTDIvol, Low Att, while normalized breast dose can also be estimated with a regional metric of CTDIvol but with a larger degree of variability than observed for lung. Effective dose normalized by DLP can be estimated with a constant multiplier. AU - Hardy, A.J.* AU - Bostani, M.* AU - McMillan, K.L.* AU - Zankl, M. AU - McCollough, C.H.* AU - Cagnon, C.H.* AU - McNitt-Gray, M.* C1 - 54136 C2 - 45355 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 4667-4682 TI - Estimating lung, breast, and effective dose from low-dose lung cancer screening CT exams with tube current modulation across a range of patient sizes. JO - Med. Phys. VL - 45 IS - 10 PB - Wiley PY - 2018 SN - 0094-2405 ER - TY - JOUR AU - Muemlller, B.S.* AU - Ryang, Y.M.* AU - Oechsner, M.* AU - Duemlsberg, M.* AU - Meyer, B.* AU - Combs, S.E. AU - Wilkens, J.J.* C1 - 53983 C2 - 45167 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - E260-E260 TI - The dosimetric impact of uncertainties in HU assignment of spinal implants for photon and proton RT: Carbon vs titanium screw systems. JO - Med. Phys. VL - 45 IS - 6 PB - Wiley PY - 2018 SN - 0094-2405 ER - TY - JOUR AB - Fluorescence-guided surgery (FGS) and other interventions are rapidly evolving as a class of technologically driven interventional approaches in which many surgical specialties visualize fluorescent molecular tracers or biomarkers through associated cameras or oculars to guide clinical decisions on pathological lesion detection and excision/ablation. The technology has been commercialized for some specific applications, but also presents technical challenges unique to optical imaging that could confound the utility of some interventional procedures where real-time decisions must be made. Accordingly, the AAPM has initiated the publication of this Blue Paper of The Emerging Technology Working Group (TETAWG) and the creation of a Task Group from the Therapy Physics Committee within the Treatment Delivery Subcommittee. In describing the relevant issues, this document outlines the key parameters, stakeholders, impacts, and outcomes of clinical FGS technology and its applications. The presentation is not intended to be conclusive, but rather to inform the field of medical physics and stimulate the discussions needed in the field with respect to a seemingly low-risk imaging technology that has high potential for significant therapeutic impact. This AAPM Task Group is working toward consensus around guidelines and standards for advancing the field safely and effectively. AU - Pogue, B.W.* AU - Zhu, T.C.* AU - Ntziachristos, V. AU - Paulsen, K.D.* AU - Wilson, B.C.* AU - Pfefer, J.* AU - Nordstrom, R.J.* AU - Litorja, M.* AU - Wabnitz, H.* AU - Chen, Y.* AU - Gioux, S.* AU - Tromberg, B.J.* AU - Yodh, A.G.* C1 - 53478 C2 - 44585 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 2681-2688 TI - Fluorescence-guided surgery and intervention - An AAPM emerging technology blue paper. JO - Med. Phys. VL - 45 IS - 6 PB - Wiley PY - 2018 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Variance-based sensitivity analysis (SA) is described and applied to the radiation dosimetry model proposed by the Committee on Medical Internal Radiation Dose (MIRD) for the organ-level absorbed dose calculations in nuclear medicine. The uncertainties in the dose coefficients thus calculated are also evaluated. Methods: A Monte Carlo approach was used to compute first-order and total-effect SA indices, which rank the input factors according to their influence on the uncertainty in the output organ doses. These methods were applied to the radiopharmaceutical (S)-4-(3-18F-fluoropropyl)-L-glutamic acid (18F-FSPG) as an example. Since18F-FSPG has 11 notable source regions, a 22-dimensional model was considered here, where 11 input factors are the time-integrated activity coefficients (TIACs) in the source regions and 11 input factors correspond to the sets of the specific absorbed fractions (SAFs) employed in the dose calculation. The SA was restricted to the foregoing 22 input factors. The distributions of the input factors were built based on TIACs of five individuals to whom the radiopharmaceutical18F-FSPG was administered and six anatomical models, representing two reference, two overweight, and two slim individuals. The self-absorption SAFs were mass-scaled to correspond to the reference organ masses. Results: The estimated relative uncertainties were in the range 10%–30%, with a minimum and a maximum for absorbed dose coefficients for urinary bladder wall and heart wall, respectively. The applied global variance-based SA enabled us to identify the input factors that have the highest influence on the uncertainty in the organ doses. With the applied mass-scaling of the self-absorption SAFs, these factors included the TIACs for absorbed dose coefficients in the source regions and the SAFs from blood as source region for absorbed dose coefficients in highly vascularized target regions. For some combinations of proximal target and source regions, the corresponding cross-fire SAFs were found to have an impact. Conclusion: Global variance-based SA has been for the first time applied to the MIRD schema for internal dose calculation. Our findings suggest that uncertainties in computed organ doses can be substantially reduced by performing an accurate determination of TIACs in the source regions, accompanied by the estimation of individual source region masses along with the usage of an appropriate blood distribution in a patient's body and, in a few cases, the cross-fire SAFs from proximal source regions. AU - Zvereva, A. AU - Kamp, F.* AU - Schlattl, H. AU - Zankl, M. AU - Parodi, K.* C1 - 53548 C2 - 44890 CY - 111 River St, Hoboken 07030-5774, Nj Usa SP - 3391-3403 TI - Impact of interpatient variability on organ dose estimates according to MIRD schema: Uncertainty and variance-based sensitivity analysis. JO - Med. Phys. VL - 45 IS - 7 PB - Wiley PY - 2018 SN - 0094-2405 ER - TY - JOUR AU - Hardy, A.* AU - McMillan, K.L.* AU - Bostani, M.* AU - Zankl, M. AU - McCollough, C.H.* AU - Cagnon, C.H.* AU - McNitt-Gray, M.* C1 - 53287 C2 - 44525 CY - Hoboken SP - 3315-3316 TI - Generating K-factors to estimate effective dose for CT exams that account for patient size and tube current modulation. JO - Med. Phys. VL - 44 IS - 6 PB - Wiley PY - 2017 SN - 0094-2405 ER - TY - JOUR AU - Hardy, A.* AU - Bostani, M.* AU - Zankl, M. AU - McCollough, C.H.* AU - Cagnon, C.H.* AU - McNitt-Gray, M.* C1 - 53288 C2 - 44524 CY - Hoboken SP - 3314-3315 TI - Determining size-specific dose estimates for head CT examinations. JO - Med. Phys. VL - 44 IS - 6 PB - Wiley PY - 2017 SN - 0094-2405 ER - TY - JOUR AU - Ispir, B.* AU - Sarigul, N.* AU - Yenice, K.* AU - Schlattl, H. AU - Yegingil, Z.* C1 - 53286 C2 - 44527 CY - Hoboken SP - 2910-2910 TI - A Monte Carlo evaluation of flattening-filter-free MV photon dose distribution in the presence of high-Z metals. JO - Med. Phys. VL - 44 IS - 6 PB - Wiley PY - 2017 SN - 0094-2405 ER - TY - JOUR AB - BACKGROUND AND PURPOSE: Systematic investigation of the energy and angular dependence of secondary neutron fluence energy distributions and ambient dose equivalents values (H*(10)) inside a pencil beam scanning proton therapy treatment room using a gantry. MATERIAL AND METHODS: Neutron fluence energy distributions were measured with an extended-range Bonner sphere spectrometer featuring ³He proportional counters, at four positions at 0°, 45°, 90° and 135° with respect to beam direction and at a distance of 2 m from the isocenter. The energy distribution of secondary neutrons was investigated for initial proton beam energies of 75 MeV, 140 MeV and 200 MeV, respectively, using a 2D scanned irradiation field of 11 x 11 cm² delivered to a 30 x 30 x 30 cm³ PMMA phantom. Additional measurements were performed at a proton energy of 118 MeV including a 5 cm range-shifter (PMMA), yielding a Bragg peak position similar to that of 75 MeV protons. RESULTS: Ambient dose equivalent values from 0.3 μSv/ Gy (75 MeV; 90°) to 24 μSv/Gy (200 MeV; 0°) were measured inside the treatment room at a distance of 2 m from the isocenter. H*(10) values were lower (by factors of up to 7.2 (at 45°)) at 75 MeV compared to those at 118 MeV with the 5 cm range-shifter. At 0° and 45° an evaporation peak was found in the measured neutron fluence energy distributions, at neutron energies around MeV, which contributes about 50% to total H*(10) values, for all investigated proton beam energies. CONCLUSIONS: This study showed a pronounced increase of secondary neutron H*(10) values inside the proton treatment room with increasing proton energy without beam modifiers. For example, in beam direction this increase was about a factor of 50 when protons of 75 MeV and 200 MeV were compared. The existence of a peak of secondary neutrons in the MeV region was demonstrated in beam direction (0°). This peak is due to evaporation neutrons produced in the existing surrounding materials such as those used for the gantry. Therefore, any simulation of the secondary neutrons within a proton treatment room must take these materials into account. In addition, the results obtained here show that the use of a range-shifter increases the production of secondary neutrons inside the treatment room. Using a range-shifter the higher neutron doses observed mainly result from the higher incident proton energy (118 MeV instead of 75 MeV when no range-shifter was used), due to higher neutron production cross-sections. AU - Trinkl, S. AU - Mares, V. AU - Englbrecht, F.S.* AU - Wilkens, J.J.* AU - Wielunski, M. AU - Parodi, K.* AU - Rühm, W. AU - Hillbrand, M.* C1 - 50716 C2 - 42700 CY - Hoboken SP - 1912-1920 TI - Systematic out-of-field secondary neutron spectrometry and dosimetry in pencil beam scanning proton therapy. JO - Med. Phys. VL - 44 IS - 5 PB - Wiley PY - 2017 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: Range verification in ion beam therapy relies to date on nuclear imaging techniques which require complex and costly detector systems. A different approach is the detection of thermoacoustic signals that are generated due to localized energy loss of ion beams in tissue (ionoacoustics). Aim of this work was to study experimentally the achievable position resolution of ionoacoustics under idealized conditions using high frequency ultrasonic transducers and a specifically selected probing beam. METHODS: A water phantom was irradiated by a pulsed 20 MeV proton beam with varying pulse intensity and length. The acoustic signal of single proton pulses was measured by different PZT-based ultrasound detectors (3.5 and 10 MHz central frequencies). The proton dose distribution in water was calculated by Geant4 and used as input for simulation of the generated acoustic wave by the matlab toolbox k-WAVE. RESULTS: In measurements from this study, a clear signal of the Bragg peak was observed for an energy deposition as low as 10(12) eV. The signal amplitude showed a linear increase with particle number per pulse and thus, dose. Bragg peak position measurements were reproducible within ±30 μm and agreed with Geant4 simulations to better than 100 μm. The ionoacoustic signal pattern allowed for a detailed analysis of the Bragg peak and could be well reproduced by k-WAVE simulations. CONCLUSIONS: The authors have studied the ionoacoustic signal of the Bragg peak in experiments using a 20 MeV proton beam with its correspondingly localized energy deposition, demonstrating submillimeter position resolution and providing a deep insight in the correlation between the acoustic signal and Bragg peak shape. These results, together with earlier experiments and new simulations (including the results in this study) at higher energies, suggest ionoacoustics as a technique for range verification in particle therapy at locations, where the tumor can be localized by ultrasound imaging. This acoustic range verification approach could offer the possibility of combining anatomical ultrasound and Bragg peak imaging, but further studies are required for translation of these findings to clinical application. AU - Assmann, W.* AU - Kellnberger, S. AU - Reinhardt, S.* AU - Lehrack, S.* AU - Edlich, A.* AU - Thirolf, P.G.* AU - Moser, M.* AU - Dollinger, G.* AU - Omar, M. AU - Ntziachristos, V. AU - Parodi, K.* C1 - 43231 C2 - 36283 CY - Melville SP - 567-574 TI - Ionoacoustic characterization of the proton Bragg peak with submillimeter accuracy. JO - Med. Phys. VL - 42 IS - 2 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - Purpose: To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors. Methods: Working Group 9 of the European Radiation Dosimetry Group (EURADOS WG9-Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended-range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H∗(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs-tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem-counters (WENDI-II, LB 6411, RadEye™ NL, a regular and an extended-range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low-lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH-40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm3) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm2 field size. Results: Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H∗(10) value of ∼51 μSvGy-1; this was measured at 1.15 m along the beam axis. H∗(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy-1 at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy-1). Finally, the agreement on H∗(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem-counters (LB 6411, RadEye™ NL, NM2-458) underestimated the H∗(10) by up to a factor of 4, Hawk TEPCs and the WENDI-II range-extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient. Conclusions: Extended-range BSS, TEPCs, and the WENDI-II enable accurate measurements of stray neutrons while other rem-counters are not appropriate considering the high-energy range of neutrons involved in proton therapy. AU - Farah, J.* AU - Mares, V. AU - Romero-Expósito, M.* AU - Trinkl, S. AU - Domingo, C.* AU - Dufek, V.* AU - Klodowska, M.* AU - Kubančák, J.* AU - Knezevic, Z.* AU - Liszka, M.* AU - Majer, M.* AU - Miljanić, S.* AU - Ploc, O.* AU - Schinner, K. AU - Stolarczyk, L.* AU - Trompier, F.* AU - Wielunski, M. AU - Olko, P.* AU - Harrison, R.M.* C1 - 44819 C2 - 37051 CY - Melville SP - 2572-2584 TI - Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 intercomparison exercise of active dosimetry systems. JO - Med. Phys. VL - 42 IS - 5 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: We present a validation study of a morphological NTCP model predicting dry mouth syndrome (xerostomia) based on the spatial distribution of the dose received by salivary the glands in head-and-neck cancer patients during radiation therapy. METHODS: We examined a recently proposed model based on Bayesian multivariate logistic regression. It uses scale-invariant moments of the three-dimensional dose distribution to explicitly include information about the distribution of the dose within the parotid glands in different spatial directions. We tested the classification performance of this model on our independent patient cohort and compared it to routinely used clinical mean dose models. The predictive power of the models was evaluated using receiver operating characteristics (ROC). RESULTS: The study comprised 105 head-and-neck cancer patients from varying tumor sites. Of these patients, 13 reported severe xerostomia between five and 48 months after radiation therapy. The AUC of the morphological model, the mean-dose model based on the contralateral parotid gland, and the mean-dose model based on both parotid glands were 0.79, 0.71, and 0.69 respectively. The morphological model performed better than the model based on the mean-dose in the contralateral gland (p-value=0.04) as well as the model based on the mean-dose in both parotid glands (p-value=0.05). Preliminary results regarding the underlying feature selection reconfirm the high predictive power of the second moment, i.e. the spread of the dose, in cranio-caudal direction within the contralateral parotid gland. CONCLUSION: Our study confirms the benefit of spatial dose information over volumetric dose information for the prediction of xerostomia after radiation therapy. Incorporation of such morphological models during treatment planning could improve the evidence for clinical decision making and patients' quality of life after treatment. In the future, we will explore the possibility to additionally incorporate parotid shrinkage, tumor regression, uncertainties stemming from imperfect delineations, patient positioning and organ motion. AU - Gabrys, H.* AU - Buettner, F. AU - Schubert, K.* AU - Mescher, H.* AU - Debus, J.* AU - Sterzing, F.* AU - Bangert, M.* C1 - 45674 C2 - 37412 TI - TH-AB-304-12: Validation of a morphological xerostomia prediction model. JO - Med. Phys. VL - 42 IS - 6 PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: With recent advancement in hardware of optoacoustic imaging systems, highly detailed cross-sectional images may be acquired at a single laser shot, thus eliminating motion artifacts. Nonetheless, other sources of artifacts remain due to signal distortion or out-of-plane signals. The purpose of image reconstruction algorithms is to obtain the most accurate images from noisy, distorted projection data. METHODS: In this paper, the authors use the model-based approach for acoustic inversion, combined with a sparsity-based inversion procedure. Specifically, a cost function is used that includes the L1 norm of the image in sparse representation and a total variation (TV) term. The optimization problem is solved by a numerically efficient implementation of a nonlinear gradient descent algorithm. TV-L1 model-based inversion is tested in the cross section geometry for numerically generated data as well as for in vivo experimental data from an adult mouse. RESULTS: In all cases, model-based TV-L1 inversion showed a better performance over the conventional Tikhonov regularization, TV inversion, and L1 inversion. In the numerical examples, the images reconstructed with TV-L1 inversion were quantitatively more similar to the originating images. In the experimental examples, TV-L1 inversion yielded sharper images and weaker streak artifact. CONCLUSIONS: The results herein show that TV-L1 inversion is capable of improving the quality of highly detailed, multiscale optoacoustic images obtained in vivo using cross-sectional imaging systems. As a result of its high fidelity, model-based TV-L1 inversion may be considered as the new standard for image reconstruction in cross-sectional imaging. AU - Han, Y. AU - Tzoumas, S. AU - Nunes, A. AU - Ntziachristos, V. AU - Rosenthal, A. C1 - 46726 C2 - 37766 CY - Melville SP - 5444-5452 TI - Sparsity-based acoustic inversion in cross-sectional multiscale optoacoustic imaging. JO - Med. Phys. VL - 42 IS - 9 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - Purpose: A prior image based temporally constrained reconstruction (PITCR) algorithm was developed for obtaining accurate temperature maps having better volume coverage, and spatial, and temporal resolution than other algorithms for highly undersampled data in magnetic resonance (MR) thermometry. Methods: The proposed PITCR approach is an algorithm that gives weight to the prior image and performs accurate reconstruction in a dynamic imaging environment. The PITCR method is compared with the temporally constrained reconstruction (TCR) algorithm using pork muscle data. Results: The PITCR method provides superior performance compared to the TCR approach with highly undersampled data. The proposed approach is computationally expensive compared to the TCR approach, but this could be overcome by the advantage of reconstructing with fewer measurements. In the case of reconstruction of temperature maps from 16% of fully sampled data, the PITCR approach was 1.57× slower compared to the TCR approach, while the root mean square error using PITCR is 0.784 compared to 2.815 with the TCR scheme. Conclusions: The PITCR approach is able to perform more accurate reconstructions of temperature maps compared to the TCR approach with highly undersampled data in MR guided high intensity focused ultrasound. AU - Prakash, J. AU - Todd, N.* AU - Yalavarthy, P.K.* C1 - 47374 C2 - 40511 SP - 6804-6814 TI - Prior image based temporally constrained reconstruction algorithm for magnetic resonance guided high intensity focused ultrasound. JO - Med. Phys. VL - 42 IS - 12 PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Reconstruction of x-ray computed tomography (CT) data remains a mathematically challenging problem in medical imaging. Complementing the standard analytical reconstruction methods, sparse regularization is growing in importance, as it allows inclusion of prior knowledge. The paper presents a method for sparse regularization based on the curvelet frame for the application to iterative reconstruction in x-ray computed tomography. Methods: In this work, the authors present an iterative reconstruction approach based on the alternating direction method of multipliers using curvelet sparse regularization. Results: Evaluation of the method is performed on a specifically crafted numerical phantom dataset to highlight the method’s strengths. Additional evaluation is performed on two real datasets from commercial scanners with different noise characteristics, a clinical bone sample acquired in a micro-CT and a human abdomen scanned in a diagnostic CT. The results clearly illustrate that curvelet sparse regularization has characteristic strengths. In particular, it improves the restoration and resolution of highly directional, high contrast features with smooth contrast variations. The authors also compare this approach to the popular technique of total variation and to traditional filtered backprojection. Conclusions: The authors conclude that curvelet sparse regularization is able to improve reconstruction quality by reducing noise while preserving highly directional features.   AU - Wieczorek, M.* AU - Frikel, J. AU - Vogel, J.* AU - Eggl, E.* AU - Kopp, F.* AU - Noel, P.B.* AU - Pfeiffer, F.* AU - Demaret, L. AU - Lasser, T.* C1 - 43859 C2 - 36611 CY - Melville SP - 1555-1565 TI - X-ray computed tomography using curvelet sparse regularization. JO - Med. Phys. VL - 42 IS - 4 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2015 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Speed of sound difference in the imaged object and surrounding coupling medium may reduce the resolution and overall quality of optoacoustic tomographic reconstructions obtained by assuming a uniform acoustic medium. In this work, the authors investigate the effects of acoustic heterogeneities and discuss potential benefits of accounting for those during the reconstruction procedure. Methods: The time shift of optoacoustic signals in an acoustically heterogeneous medium is studied theoretically by comparing different continuous and discrete wave propagation models. A modification of filtered back-projection reconstruction is subsequently implemented by considering a straight acoustic rays model for ultrasound propagation. The results obtained with this reconstruction procedure are compared numerically and experimentally to those obtained assuming a heuristically fitted uniform speed of sound in both full-view and limited-view optoacoustic tomography scenarios. Results: The theoretical analysis showcases that the errors in the time-of-flight of the signals predicted by considering the straight acoustic rays model tend to be generally small. When using this model for reconstructing simulated data, the resulting images accurately represent the theoretical ones. On the other hand, significant deviations in the location of the absorbing structures are found when using a uniform speed of sound assumption. The experimental results obtained with tissue-mimicking phantoms and a mouse postmortem are found to be consistent with the numerical simulations. Conclusions: Accurate analysis of effects of small speed of sound variations demonstrates that accounting for differences in the speed of sound allows improving optoacoustic reconstruction results in realistic imaging scenarios involving acoustic heterogeneities in tissues and surrounding media.   AU - Dean-Ben, X.L. AU - Ntziachristos, V. AU - Razansky, D. C1 - 31716 C2 - 34681 CY - Melville TI - Effects of small variations of speed of sound in optoacoustic tomographic imaging. JO - Med. Phys. VL - 41 IS - 7 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2014 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Image quantification in optoacoustic tomography implies the use of accurate forward models of excitation, propagation, and detection of optoacoustic signals while inversions with high spatial resolution usually involve very large matrices, leading to unreasonably long computation times. The development of fast and memory efficient model-based approaches represents then an important challenge to advance on the quantitative and dynamic imaging capabilities of tomographic optoacoustic imaging.Methods: Herein, a method for simplification and acceleration of model-based inversions, relying on inherent symmetries present in common tomographic acquisition geometries, has been introduced. The method is showcased for the case of cylindrical symmetries by using polar image discretization of the time-domain optoacoustic forward model combined with efficient storage and inversion strategies.Results: The suggested methodology is shown to render fast and accurate model-based inversions in both numerical simulations and post mortem small animal experiments. In case of a full-view detection scheme, the memory requirements are reduced by one order of magnitude while high-resolution reconstructions are achieved at video rate.Conclusions: By considering the rotational symmetry present in many tomographic optoacoustic imaging systems, the proposed methodology allows exploiting the advantages of model-based algorithms with feasible computational requirements and fast reconstruction times, so that its convenience and general applicability in optoacoustic imaging systems with tomographic symmetries is anticipated. AU - Lutzweiler, C. AU - Dean-Ben, X.L. AU - Razansky, D. C1 - 29073 C2 - 33619 TI - Expediting model-based optoacoustic reconstructions with tomographic symmetries. JO - Med. Phys. VL - 41 IS - 1 PY - 2014 SN - 0094-2405 ER - TY - JOUR AB - Patients undergoing body CT examinations. This investigation extends that work to head CT exams by using Monte Carlo simulations to develop size-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients. Methods: Using eight patient models from the GSF family of voxelized phantoms, dose to the brain and lens of the eye was estimated using Monte Carlo simulations of contiguous axial and helical scans for 64-slice multidetector CT scanners from four major manufacturers. For each patient model and scan mode, scanner-independent CTDIvol-to-organ-dose conversion coefficients were calculated by normalizing organ dose by scanner-specific 16 cm CTDIvol values and averaging across all scanners. Head size was measured using both geometric and attenuation-based size metrics. Head perimeter and effective diameter (ED), both geometric size metrics, were measured directly from the GSF data at the first slice superior to the eyes. Because the GSF models pixel data are provided in terms of organ identification numbers instead of CT numbers, an indirect estimate of water equivalent diameter (WED), an attenuation-based size metric, was determined based on the relationships between WED and both ED and perimeter for a sample of patient data. Correlations between CTDIvol-to-organ-dose conversion coefficients and the various patient size metrics were then explored. Results: The analysis of the patient data revealed a best-fit linear relationship (R2 of 0.87) between ED and WED across a wide variety of patient sizes. Using this relationship along with ED determined from the GSF data, WED was estimated for each GSF model. An exponential relationship between CTDIvol normalized organ dose and WED was observed for both contiguous axial and helical scanning. For head perimeter and ED measured directly from the GSF data, an exponential relationship between CTDIvol normalized organ dose and patient size was also observed for each scan mode. For all patient size metrics and scan modes, R2 of the exponential fits ranged from 0.92 to 0.93 and 0.73 to 0.85 for the brain and lens of the eye, respectively. Conclusions: For all scan modes, strong correlation exists between CTDIvol normalized brain dose and both geometric and attenuation-based patient size metrics. A slightly lower correlation between CTDIvol normalized organ dose and patient size was observed for the lens of the eye. This may be due to the combination of the eye lens being a small peripheral organ and the presence of surface dose variation in both contiguous axial and helical scanning. Results indicate that robust estimates of patient-specific head CT dose may be provided using the size-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients described in this work. AU - McMillan, K.L.* AU - Bostani, M.* AU - Cagnon, C.H.* AU - Zankl, M. AU - Sepahdari, A.R.* AU - McNitt-Gray, M.F.* C1 - 42901 C2 - 35805 TI - Size-specific, scanner-independent organ dose estimates in contiguous axial and helical head CT examinations. JO - Med. Phys. VL - 41 IS - 12 PY - 2014 SN - 0094-2405 ER - TY - JOUR AB - One of the major challenges in dynamic multispectral optoacoustic imaging is its relatively low signal-to-noise ratio which often requires repetitive signal acquisition and averaging, thus limiting imaging rate. The development of denoising methods which prevent the need for signal averaging in time presents an important goal for advancing the dynamic capabilities of the technology. Methods: In this paper, a denoising method is developed for multispectral optoacoustic imaging which exploits the implicit sparsity of multispectral optoacoustic signals both in space and in spectrum. Noise suppression is achieved by applying thresholding on a combined wavelet-Karhunen–Loève representation in which multispectral optoacoustic signals appear particularly sparse. The method is based on inherent characteristics of multispectral optoacoustic signals of tissues, offering promise for general application in different incarnations of multispectral optoacoustic systems. Results: The performance of the proposed method is demonstrated on mouse images acquired in vivo for two common additive noise sources: time-varying parasitic signals and white noise. In both cases, the proposed method shows considerable improvement in image quality in comparison to previously published denoising strategies that do not consider multispectral information. Conclusions: The suggested denoising methodology can achieve noise suppression with minimal signal loss and considerably outperforms previously proposed denoising strategies, holding promise for advancing the dynamic capabilities of multispectral optoacoustic imaging while retaining image quality.   AU - Tzoumas, S. AU - Rosenthal, A. AU - Lutzweiler, C. AU - Razansky, D. AU - Ntziachristos, V. C1 - 32599 C2 - 35154 TI - Spatiospectral denoising framework for multispectral optoacoustic imaging based on sparse signal representation. JO - Med. Phys. VL - 41 IS - 11 PY - 2014 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Optoacoustic imaging relies on the detection of ultrasonic waves induced by laser pulse excitations to map optical absorption in biological tissue. A tomographic geometry employing a conventional ultrasound linear detector array for volumetric optoacoustic imaging is reported. The geometry is based on a translate-rotate scanning motion of the detector array, and capitalizes on the geometrical characteristics of the transducer assembly to provide a large solid angular detection aperture. A system for three-dimensional whole-body optoacoustic tomography of small animals is implemented. Methods: The detection geometry was tested using a 128-element linear array (5.0/7.0MHz, Acuson L7, Siemens), moved by steps with a rotation/translation stage assembly. Translation and rotation range of 13.5 mm and 180 degrees, respectively, were implemented. Optoacoustic emissions were induced in tissue-mimicking phantoms and ex vivo mice using a pulsed laser operating in the near-IR spectral range at 760 nm. Volumetric images were formed using a filtered backprojection algorithm. Results: The resolution of the optoacoustic tomography system was measured to be better than 130 mu m in-plane and 330 mu m in elevation (full width half maximum), and to be homogenous along a 15 mm diameter cross section due to the translate-rotate scanning geometry. Whole-body volumetric optoacoustic images of mice were performed ex vivo, and imaged organs and blood vessels through the intact abdominal and head regions were correlated to the mouse anatomy. Conclusions: Overall, the feasibility of three-dimensional and high-resolution whole-body optoacoustic imaging of small animal using a conventional linear array was demonstrated. Furthermore, the scanning geometry may be used for other linear arrays and is therefore expected to be of great interest for optoacoustic tomography at macroscopic and mesoscopic scale. Specifically, conventional detector arrays with higher central frequencies may be investigated. AU - Gateau, J. AU - Caballero, M.A.A. AU - Dima, A. AU - Ntziachristos, V. C1 - 22415 C2 - 30900 TI - Three-dimensional optoacoustic tomography using a conventional ultrasound linear detector array: Whole-body tomographic system for small animals. JO - Med. Phys. VL - 40 IS - 1 PB - Amer. Assoc. Physicists Medicine Amer. Inst. Physics PY - 2013 SN - 0094-2405 ER - TY - JOUR AB - Purpose: CT neuroperfusion examinations are capable of delivering high radiation dose to the skin or lens of the eyes of a patient and can possibly cause deterministic radiation injury. The purpose of this study is to: (a) estimate peak skin dose and eye lens dose from CT neuroperfusion examinations based on several voxelized adult patient models of different head size and (b) investigate how well those doses can be approximated by some commonly used CT dose metrics or tools, such as CTDIvol, American Association of Physicists in Medicine (AAPM) Report No. 111 style peak dose measurements, and the ImPACT organ dose calculator spreadsheet.Methods: Monte Carlo simulation methods were used to estimate peak skin and eye lens dose on voxelized patient models, including GSF's Irene, Frank, Donna, and Golem, on four scanners from the major manufacturers at the widest collimation under all available tube potentials. Doses were reported on a per 100 mAs basis. CTDIvol measurements for a 16 cm CTDI phantom, AAPM Report No. 111 style peak dose measurements, and ImPACT calculations were performed for available scanners at all tube potentials. These were then compared with results from Monte Carlo simulations.Results: The dose variations across the different voxelized patient models were small. Dependent on the tube potential and scanner and patient model, CTDIvol values overestimated peak skin dose by 26%-65%, and overestimated eye lens dose by 33%-106%, when compared to Monte Carlo simulations. AAPM Report No. 111 style measurements were much closer to peak skin estimates ranging from a 14% underestimate to a 33% overestimate, and with eye lens dose estimates ranging from a 9% underestimate to a 66% overestimate. The ImPACT spreadsheet overestimated eye lens dose by 2%-82% relative to voxelized model simulations.Conclusions: CTDIvol consistently overestimates dose to eye lens and skin. The ImPACT tool also overestimated dose to eye lenses. As such they are still useful as a conservative predictor of dose for CT neuroperfusion studies. AAPM Report No. 111 style measurements are a better predictor of both peak skin and eye lens dose than CTDIvol and ImPACT for the patient models used in this study. It should be remembered that both the AAPM Report No. 111 peak dose metric and CTDIvol dose metric are dose indices and were not intended to represent actual organ doses. AU - Zhang, D.* AU - Cagnon, C.H.* AU - Villablanca, J.P.* AU - McCollough, C.H.* AU - Cody, D.D.* AU - Zankl, M. AU - DeMarco, J.J.* AU - McNitt-Gray, M.F.* C1 - 27560 C2 - 32721 TI - Estimating peak skin and eye lens dose from neuroperfusion examinations: Use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM report no. 111, and ImPACT dosimetry tool values. JO - Med. Phys. VL - 40 IS - 9 PB - Amer. Assoc. Physicists Medicine Amer. Inst. Physics PY - 2013 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Quality assurance in computed tomography (CT) is commonly performed with the Fourier-based modulation transfer function (MTF) and the noise variance, while more recently the noise power spectrum (NPS) has increased in popularity. The Fourier-based methods make assumptions such as shift-invariance and cyclostationarity. These assumptions are violated in real clinical systems and consequently are expected to result in systematic errors. A spatial approach, based on the object transfer matrix (T) and the covariance matrix (K) theory, does not require these assumptions and can provide a more general description of the imaging system. In this paper, the authors present an experimental methodology and data treatment for quality assessment of a lab cone-beam CT system by comparing the spatial with the Fourier approach in 2D reconstructed slices.Methods: In order to have control over all experimental parameters and image reconstruction, a bench-top flat-panel-based cone-beam CT scanner and a cylindrical water-filled poly(methyl methacrylate) (PMMA) phantom were used for the noise measurements. An aluminum foil inserted in the water phantom enabled the estimation of the line response function (LRF) with a limited number of assumptions. The authors evaluated the spatial blur, the noise and the signal-to-noise ratio (SNR) using the spatial approach as well as the Fourier-based approach. In order to evaluate the degree of noise nonstationarity of their cone-beam CT system, the authors evaluated both the local and global CT noise properties and compared them using both approaches.Results: For the laboratory cone-beam CT, the location-dependent noise evaluation showed that in addition to the noise variance, the NPS and covariance eigenvector symmetry depend on the location in the image. The estimated signal transfer was similar for both approaches. Unlike the Fourier approach which uses the same exponential wave function basis for both MTF and NPS, the eigenvectors of T and K were significantly different.Conclusions: By using the eigenvectors of the noise and object transfer to characterize the system, the spatial approach provides additional information to the Fourier approach and is therefore an important tool for a thorough understanding of a CT system. AU - Brunner, C.C. AU - Abboud, S.F.* AU - Hoeschen, C. AU - Kyprianou, I.S.* C1 - 7913 C2 - 29913 SP - 3214-3228 TI - Signal detection and location-dependent noise in cone-beam computed tomography using the spatial definition of the Hotelling SNR. JO - Med. Phys. VL - 39 IS - 6 PB - American Inst. of Physics PY - 2012 SN - 0094-2405 ER - TY - JOUR AB - A thorough understanding of the dose‐response of individual organs‐at‐risk is essential for being able to choose the best radiotherapy treatment for a patient. Therefore, the spatial distribution of dose to the rectum, the anal canal and the parotid glands and its role for radiation‐induced late toxicities were assessed by performing a retrospective analysis of data from the randomised controlled trials MRC RT01 and PARSPORT. Interpretable geometrical features were introduced to quantify the spatial distribution of dose and correlations between the dose to the anorectal wall and seven clinically relevant late rectal toxicities were assessed. Novel risk‐factors based on the spatial distribution of dose could be identified for different endpoints. It was demonstrated that the type of dose‐response relationship differed considerably between different endpoints. Rectal bleeding was more strongly correlated to the lateral extent than to any other measure, including the dose‐surface histogram (DSH). The dosimetric measure with the strongest correlation to loose stools and proctitis were longitudinal extent and DSHs respectively. Based on this statistical analysis, dosimetric constraints taking spatial information into account were derived. An interpretable, non‐linear normal‐tissue‐complication‐probability model (NTCP model) explicitly taking spatial information into account was presented and its predictive power was evaluated and compared to NTCP models used in current clinical practice. Our novel NTCP models predicted late rectal toxicities significantly better than conventional models. Using the novel NTCP models 3D dose patterns related to a low risk of complications have been identified. These dose patterns may be useful for optimising and assessing treatment plans, potentially yielding better treatments with a reduced risk of late rectal toxicities. Furthermore, the role of spatial information and clinical risk factors for xerostomia after head‐and‐neck radiotherapy was assessed. Multivariate NTCP models taking the shape and the location of the dose to the parotid glands into account were derived based on data from the PARSPORT trial. Results were externally validated using data from two independent patient cohorts. A “directed” bath‐and‐shower effect was identified, indicating that a high relative concentration of the dose in the medial‐inferior part of the ipsi‐lateral gland and a high skewness of the dose in cranio‐caudal direction in the superficial lobe of the ipsi‐lateral parotid are beneficial for patients in terms of reducing the risk of xerostomia. Our novel NTCP model taking the “directed” bath‐and‐shower effect into account can be used to rank treatment plans more reliably than standard mean‐dose models. We have also shown that it is possible to implement this model in an inverse‐treatment‐planning system and take morphological information into account when generating IMRT treatment plans. Learning Objectives: 1. Understand issues related to quantifying the spatial distribution of dose to organs‐at risk 2. Understand issues related to generating and validating NTCP models based on these risk‐factors 3. Understand issues related to identifying risk factors related to the spatial distribution of dose. AU - Buettner, F. C1 - 51613 C2 - 0 SP - 3901-3902 TI - TU‐C‐BRA‐02: The Relevance of the Spatial Distribution of Dose for Complications after Head and Neck and Prostate Radiotherapy. JO - Med. Phys. VL - 39 IS - 6 PY - 2012 SN - 0094-2405 ER - TY - JOUR AB - Purpose: To investigate the effects of an endorectal device during prostate radiotherapy on the spatial distribution of dose to the ano‐rectal region and quantify implications for normal‐tissue‐complication probabilities. Methods: Twenty‐three patients with localised prostate cancer, referred for external beam radiotherapy had 2 CT scans acquired, without and with the rectal obturator (ProSpare) in‐situ. For each patient two dose distributions were generated, based on both CT scans. Dose‐surface maps for the rectal surface and the anal surface were generated and mean dose as well as a spatial measure (circumference of the dose distribution) were determined for all patients, with and without ProSpare. Using previously published NTCP models, the effect of ProSpare on NTCP was investigated for rectal bleeding and subjective sphincter control. Results: In a previous study subjective sphincter control correlated strongest with mean dose and lateral extent at 53 Gy. The use of ProSpare resulted in a highly significant reduction of the lateral extent at 53 Gy (p=0.006), mean dose (p=0.0009) and NTCP according to the LKB model (p=0.002 for grade 2 and p=0.001 for grade > =1). In a previous study we reported that rectal bleeding correlated most strongly with the lateral extent at 55 Gy and presented the constraint that it should not exceed 42% of the circumference. Using ProSpare resulted in a significant reduction of the lateral extent at 55 Gy (p=0.001) and significantly more patients met that proposed constraint (p=0.047). ProSpare resulted in a significant reduction of NTCP for grade‐2 rectal bleeding (p=0.007) and a reduction for rectal bleeding grade > =1 (p=0.053). Conclusions: ProSpare resulted in a significant reduction of mean dose to the anal sphincter and a significant reduction of the lateral extent at 55 Gy. This corresponded to a significant reduction in the predicted risk of reporting subjective sphincter control and grade‐2 rectal bleeding. AU - Buettner, F. AU - Alexander, E.* AU - Mcnair, H.* AU - Gulliford, S.* AU - Partridge, M.* AU - Dearnaley, D.* C1 - 51616 C2 - 0 SP - 3762-3762 TI - SU‐E‐T‐255: A Novel Rectal Obturator for Prostate Radiotherapy Improves the Spatial Distribution of Dose and Reduces the Predicted Risk for Rectal Bleeding and Subjective Sphincter Control. JO - Med. Phys. VL - 39 IS - 6 PY - 2012 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Near-field radiofrequency thermoacoustic (NRT) tomography has been recently introduced for imaging electromagnetic (EM) properties of tissues using ultrawideband, high-energy impulses, which induce thermoacoustic responses. Operation in the near-field allows for more effective energy coupling into tissue, compared to using radiating sources, which in turn enables the use of shorter excitation pulses and leads to higher image resolution. This work aimed at investigating transmission lines as a method to generate excitation pulses to improve the NRT resolution over previous implementations without compromising the energy coupled into tissue. Methods: The authors implemented a number of custom-made transmission lines to overcome the challenges of the broadband nature of the impulse excitation required in NRT. The authors further constructed phantoms and investigated the performance of the lines in regard to the pulse duration, energy coupling and the resulting resolution, and image quality achieved. Finally, the authors employed mice in order to investigate the performance of the approach in tissue imaging. Results: The authors found that the use of transmission lines resulted in the generation of RF impulses in the range of tens of nanoseconds and shorter. This performance resulted to resolution improvements over previous thermoacoustic imaging implementations, reaching 45 mu m resolution, while retaining several tens to hundreds of milli-Joules of energy per pulse. This performance further allowed the visualization and clear differentiation of different mouse structures such as the heart, lung, or spinal cord. Conclusions: The use of transmission lines significantly improved the NRT performance leading to high thermoacoustic tomography imaging quality by coupling adequate amounts of energy within short times at a relatively low cost. AU - Omar, M. AU - Kellnberger, S. AU - Sergiadis, G.* AU - Razansky, D. AU - Ntziachristos, V. C1 - 8443 C2 - 30172 SP - 4460-4466 TI - Near-field thermoacoustic imaging with transmission line pulsers. JO - Med. Phys. VL - 39 IS - 7 PB - Amer. Assoc. Physicists Medicine Amer. Inst. Physics PY - 2012 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Optoacoustic imaging is an emerging noninvasive imaging modality that can resolve optical contrast through several millimeters to centimeters of tissue with diffraction-limited resolution of ultrasound. Yet, quantified reconstruction of tissue absorption maps requires optoacoustic signals to be collected from as many locations around the object as possible. In many tomographic imaging scenarios, however, only limited-view or partial projection data are available, which has been shown to generate image artifacts and overall loss of quantification accuracy. In this article, the recently introduced interpolated-matrix-model optoacoustic inversion method is tested in different limited-view scenarios and compared to the standard backprojection algorithm. Both direct (TGSVD) and iterative (PLSQR) regularization methods are proposed to improve the accuracy of image reconstructions with their performance tested on simulated and experimental data. While for full-view tomographic data the model-based inversion has been generally shown to attain higher reconstruction accuracy compared to backprojection algorithms, the incomplete tomographic datasets lead to ill-conditioned forward matrices and, consequently, to error-prone inversions, with strong artifacts following a distinct ripple-type pattern. The proposed regularization techniques are shown to stabilize the inversion and eliminate the artifacts. Overall, it has been determined that the regularized interpolated-matrix-model-based optoacoustic inversions show higher accuracy than reconstructions with the standard backprojection algorithm. Finally, the combination of model-based inversion with PLSQR or TGSVD regularization methods can lead to an accurate reconstruction of limited-projection angle optoacoustic data and practical systems for optoacoustic imaging in many realistic cases where the full-view dataset is unavailable. AU - Bühler, A. AU - Rosenthal, A. AU - Jetzfellner, T. AU - Dima, A. AU - Razansky, D. AU - Ntziachristos, V. C1 - 5043 C2 - 28450 CY - Lancaster, Pa. SP - 1694-1704 TI - Model-based optoacoustic inversions with incomplete projection data. JO - Med. Phys. VL - 38 IS - 3 PB - American Assn. of Physicists in Medicine by American Institute of Physics PY - 2011 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: Optoacoustic imaging enables mapping the optical absorption of biological tissue using optical excitation and acoustic detection. Although most image-reconstruction algorithms are based on the assumption of a detector with an isotropic sensitivity, the geometry of the detector often leads to a response with spatially dependent magnitude and bandwidth. This effect may lead to attenuation or distortion in the recorded signal and, consequently, in the reconstructed image. METHODS: Herein, an accurate numerical method for simulating the spatially dependent response of an arbitrary-shape acoustic transducer is presented. The method is based on an analytical solution obtained for a two-dimensional line detector. The calculated response is incorporated in the forward model matrix of an optoacoustic imaging setup using temporal convolution, and image reconstruction is performed by inverting the matrix relation. RESULTS: The method was numerically and experimentally demonstrated in two dimensions for both flat and focused transducers and compared to the spatial-convolution method. In forward simulations, the developed method did not suffer from the numerical errors exhibited by the spatial-convolution method. In reconstruction simulations and experiments, the use of both temporal-convolution and spatial-convolution methods lead to an enhancement in resolution compared to a reconstruction with a point detector model. However, because of its higher modeling accuracy, the temporal-convolution method achieved a noise figure approximated three times lower than the spatial-convolution method. CONCLUSIONS: The demonstrated performance of the spatial-convolution method shows it is a powerful tool for reducing reconstruction artifacts originating from the detector finite size and improving the quality of optoacoustic reconstructions. Furthermore, the method may be used for assessing new system designs. Specifically, detectors with nonstandard shapes may be investigated. AU - Rosenthal, A. AU - Ntziachristos, V. AU - Razansky, D. C1 - 6551 C2 - 28870 SP - 4285-4295 TI - Model-based optoacoustic inversion with arbitrary-shape detectors. JO - Med. Phys. VL - 38 IS - 7 PB - Amer Assoc Physicists Med. PY - 2011 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: A recent work has demonstrated the feasibility of estimating the dose to individual organs from multidetector CT exams using patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients. However, the previous study only investigated organ dose to a single patient model from a full-body helical CT scan. The purpose of this work was to extend the validity of this dose estimation technique to patients of any size undergoing a common clinical exam. This was done by determining the influence of patient size on organ dose conversion coefficients generated for typical abdominal CT exams. METHODS: Monte Carlo simulations of abdominal exams were performed using models of 64-slice MDCT scanners from each of the four major manufacturers to obtain dose to radiosensitive organs for eight patient models of varying size, age, and gender. The scanner-specific organ doses were normalized by corresponding CTDIvol values and averaged across scanners to obtain scanner-independent CTDIvol-to-organ-dose conversion coefficients for each patient model. In order to obtain a metric for patient size, the outer perimeter of each patient was measured at the central slice of the abdominal scan region. Then, the relationship between CTDIvol-to-organ-dose conversion coefficients and patient perimeter was investigated for organs that were directly irradiated by the abdominal scan. These included organs that were either completely ("fully irradiated") or partly ("partially irradiated") contained within the abdominal exam region. Finally, dose to organs that were not at all contained within the scan region ("nonirradiated") were compared to the doses delivered to fully irradiated organs. RESULTS: CTDIvol-to-organ-dose conversion coefficients for fully irradiated abdominal organs had a strong exponential correlation with patient perimeter. Conversely, partially irradiated organs did not have a strong dependence on patient perimeter. In almost all cases, the doses delivered to nonirradiated organs were less than 5%, on average across patient models, of the mean dose of the fully irradiated organs. CONCLUSIONS: This work demonstrates the feasibility of calculating patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients for fully irradiated organs in patients undergoing typical abdominal CT exams. A method to calculate patient-specific, scanner-specific, and exam-specific organ dose estimates that requires only knowledge of the CTDIvol for the scan protocol and the patient's perimeter is thus possible. This method will have to be extended in future studies to include organs that are partially irradiated. Finally, it was shown that, in most cases, the doses to nonirradiated organs were small compared to the dose to fully irradiated organs. AU - Turner, A.C.* AU - Zhang, D.* AU - Khatonabadi, M.* AU - Zankl, M. AU - DeMarco, J.J.* AU - Cagnon, C.H.* AU - Cody, D.D.* AU - Stevens, D.M.* AU - McCollough, C.H.* AU - McNitt-Gray, M.F.* C1 - 6339 C2 - 28484 SP - 820-829 TI - The feasibility of patient size-corrected, scanner-independent organ dose estimates for abdominal CT exams. JO - Med. Phys. VL - 38 IS - 2 PB - Am. Assoc. Phys. Med. PY - 2011 SN - 0094-2405 ER - TY - JOUR AB - Methods: Approaches that incorporate structural prior information were included in the inverse problem by adding a penalty term to the minimization function utilized for image reconstructions. Results were compared as to their performance with simulated and experimental data from a lung inflammation animal model and against the inversions achieved when not using priors. Results: The importance of using priors over stand-alone inversions is also showcased with high spatial sampling simulated and experimental data. The approach of optimal performance in resolving fluorescent biodistribution in small animals is also discussed. Conclusions: Inclusion of prior information from x-ray CT data in the reconstruction of the fluorescence biodistribution leads to improved agreement between the reconstruction and validation images for both simulated and experimental data. AU - Ale, A.B.F. AU - Schulz, R.B. AU - Sarantopoulos, A. AU - Ntziachristos, V. C1 - 904 C2 - 27152 SP - 1976-1986 TI - Imaging performance of a hybrid X-ray computed tomography-fluorescence molecular tomography system using priors. JO - Med. Phys. VL - 37 IS - 5 PB - American Assoc. of Physicists in Medicine PY - 2010 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: Imaging performance of radiofrequency and microwave-based thermoacoustic tomography systems is mainly determined by the ability to deposit a substantial amount of electromagnetic energy within ultrashort time duration. Pulses of nanosecond-range duration that can carry hundreds of millijoules energy are ideal for obtaining good signal-to-noise and spatial resolution in many biological imaging applications. However, existing implementations are based on modulated-carrier-frequency amplification solutions, which are generally costly and cannot achieve ultrahigh-peak-power requirements essential for optimal thermoacoustic signal generation. METHODS: Herein the authors suggest and experimentally validate a near-field radiofrequency tomography (NRT) method for high resolution imaging of biological tissues using ultrashort electromagnetic impulses. The solution includes a low-cost pulsing system while the imaged objects are placed in the near field of the energy-emitting aperture for improved coupling using nonradiative fields. RESULTS: In the current design, the authors were able to achieve excitation impulse energies of hundreds of millijoules with durations in the order of a few nanoseconds, corresponding to peak power levels of multiple megawatts. The phantom imaging experiments demonstrated image features with characteristic sizes of around 170 microm, but the impulse durations used herein allow in principle spatial resolutions in the order of a few tens of microns when using an appropriate ultrasonic detection bandwidth. CONCLUSIONS: The proposed NRT method makes it possible to attain very high spatial resolution without compromising the thermoacoustic signal strength. This makes the imaging performance to be limited by the available bandwidth of the ultrasonic detector rather than by the microwave pulse duration. It is overall expected that the combination of pulsed near-field coupling with optimal choice of energy dissipation elements will generate a practical modality that can scale its application to small and larger volumes alike, while optimally adjusting the resolution to match the acoustic resolution possible. Such an approach should find several applications in small animal and clinical imaging. AU - Razansky, D. AU - Kellnberger, S. AU - Ntziachristos, V. C1 - 5238 C2 - 27574 SP - 4602-4607 TI - Near-field radiofrequency thermoacoustic tomography with impulse excitation. JO - Med. Phys. VL - 37 IS - 9 PB - Amer Assoc Physicists Medicine PY - 2010 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: Monte Carlo radiation transport techniques have made it possible to accurately estimate the radiation dose to radiosensitive organs in patient models from scans performed with modern multidetector row computed tomography (MDCT) scanners. However, there is considerable variation in organ doses across scanners, even when similar acquisition conditions are used. The purpose of this study was to investigate the feasibility of a technique to estimate organ doses that would be scanner independent. This was accomplished by assessing the ability of CTDIvol measurements to account for differences in MDCT scanners that lead to organ dose differences. METHODS: Monte Carlo simulations of 64-slice MDCT scanners from each of the four major manufacturers were performed. An adult female patient model from the GSF family of voxelized phantoms was used in which all ICRP Publication 103 radiosensitive organs were identified. A 120 kVp, full-body helical scan with a pitch of 1 was simulated for each scanner using similar scan protocols across scanners. From each simulated scan, the radiation dose to each organ was obtained on a per mA s basis (mGy/mA s). In addition, CTDIvol values were obtained from each scanner for the selected scan parameters. Then, to demonstrate the feasibility of generating organ dose estimates from scanner-independent coefficients, the simulated organ dose values resulting from each scanner were normalized by the CTDIvol value for those acquisition conditions. RESULTS: CTDIvol values across scanners showed considerable variation as the coefficient of variation (CoV) across scanners was 34.1%. The simulated patient scans also demonstrated considerable differences in organ dose values, which varied by up to a factor of approximately 2 between some of the scanners. The CoV across scanners for the simulated organ doses ranged from 26.7% (for the adrenals) to 37.7% (for the thyroid), with a mean CoV of 31.5% across all organs. However, when organ doses are normalized by CTDIvoI values, the differences across scanners become very small. For the CTDIvol, normalized dose values the CoVs across scanners for different organs ranged from a minimum of 2.4% (for skin tissue) to a maximum of 8.5% (for the adrenals) with a mean of 5.2%. CONCLUSIONS: This work has revealed that there is considerable variation among modern MDCT scanners in both CTDIvol and organ dose values. Because these variations are similar, CTDIvol can be used as a normalization factor with excellent results. This demonstrates the feasibility of establishing scanner-independent organ dose estimates by using CTDIvol to account for the differences between scanners. AU - Turner, A.C.* AU - Zankl, M. AU - DeMarco, J.J.* AU - Cagnon, C.H.* AU - Zhang, D.* AU - Angel, E.* AU - Cody, D.D.* AU - Stevens, D.M.* AU - McCollough, C.H.* AU - McNitt-Gray, M.F.* C1 - 1255 C2 - 27319 SP - 1816-1825 TI - The feasibility of a scanner-independent technique to estimate organ dose from MDCT scans: Using CTDIvol to account for differences between scanners. JO - Med. Phys. VL - 37 IS - 4 PB - American Assoc. of Physicists in Medicine PY - 2010 SN - 0094-2405 ER - TY - JOUR AB - Purpose: In brain perfusion studies, the patient's head is scanned repeatedly at one location over a short period of time to monitor contrast wash in and wash out. This may result in high radiation doses to the skin and the eye lens and possibly deterministic effects. The purpose of this study is to estimate the radiation dose to skin and eye lens from brain perfusion studies under a variety of scanning conditions and to compare these to CTDIvol. Method and Materials: Skin dose and eye lens dose were estimated using Monte Carlo simulations with a detailed patient model (GSF Model Irene) and CT source models. Brain perfusion scans were simulated with axial scans using the widest available collimation at various scan locations. For each available kVp, the total mAs (mAs/rotation × number of rotations) to reach 2 Gy for eye lens and for skin was determined. Meanwhile, CTDIvol under each condition was obtained to investigate how well it predicts these doses. Results: For all kVps at four different scanners, the total number of rotations that would cause the dose to eye lens and skin reach 2Gy were calculated. For example, for a 300 mAs/rotation scan at 120kVp for scanner B, 58 rotations would result in an eye lens dose of 2Gy, and 47 rotations would result in a maximum skin dose of 2Gy. Depending on different kVp, CT scanners, and scan location, CTDIvol overestimates the eye lens dose by 46% to 18500% and it overestimates the skin dose by 25% to 82%. Conclusion: This study provides detailed information about the radiation dose to eye lens and skin from CT brain perfusion examinations. CTDIvol reported on the scanner console generally overestimates the dose to eye lens and skin. The results could help to improve the design of CT scan protocols. AU - Zhang, D.* AU - Cagnon, C.* AU - Demarco, J.* AU - Zankl, M. AU - Turner, A.* AU - Khatonabadi, M.* AU - Mcnitt‐gray, M.* C1 - 51612 C2 - 0 SP - 3373 TI - TU‐A‐201B‐04: Estimating Dose to Eye Lens and Skin from Radiation Dose from CT Brain Perfusion Examinations: Comparison to CTDIvol Values. JO - Med. Phys. VL - 37 IS - 6 PY - 2010 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Brain perfusion CT studies may result in radiation doses to the eye lens because of repeated scans that may in some cases be high enough to cause deterministic effects, such as cataracts. The purpose of this study is to investigate the eye lens dose from brain perfusion CT studies, and the dose reduction achieved by clinically practical approaches, such as moving the x‐ray beam away from the eye lens or tilting the gantry angle. Method and Materials: Eye lens doses were estimated using the Monte Carlo method with: (a) a detailed voxelized patient model including a model of the lens of the eye; and (b) detailed CT source models of a Siemens Sensation 64 scanner using the widest collimation (28.8mm) and 120 kVp tube voltage. Simulated brain perfusion axial scans were performed at various scan locations from 5.5cm above the eye lens to 5.5cm below the eye lens with 0.5cm intervals to investigate the scatter contribution to the eye lens dose. For the scan location where the eye lens is completely in the beam, the gantry was tilted at 5, 10, 15, 20, 25 and 30 degrees to study the dose reduction. Results: Eye lens dose drops dramatically as the scan location moves away. When the lenses are just outside the primary x‐ray beam, the dose is 17% of the maximum dose when they are completely in the beam. Tilting the gantry angle by 15 degree reduces the eye lens dose by 87%. Conclusion: The eye lens dose from CT perfusion examinations can be reduced by moving the beam away from the eyes since the scatter component is fairly small. When the examination has to be performed right over the location of the eyes, tilting the gantry angle is another effective method to reduce the eye lens dose. AU - Zhang, D.* AU - Cagnon, C.* AU - Demarco, J.* AU - Zankl, M. AU - Turner, A.* AU - Khatonabadi, M.* AU - Mcnitt‐gray, M.* C1 - 51614 C2 - 0 SP - 3109-3110 TI - SU‐GG‐I‐37: Reducing Eye Lens Dose during Brain Perfusion CT Examinations by Moving the Scan Location or Tilting the Gantry Angle. JO - Med. Phys. VL - 37 IS - 6 PY - 2010 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Antiprotons have become of interest in radiotherapy due to their higher peak to plateau dose ratio relative to protons and carbon ions, and a beneficial increase in RBE towards the Bragg peak as recently verified by experimental investigations of the AD‐4 collaboration at CERN. An obstacle limiting further research is the lack of a treatment planning system capable of concurrently optimizing the necessary modulation of intensity and energy, while accounting for the variation in biological effectiveness. Here we develop a Monte Carlo based treatment planning system for this purpose and subsequently quantify its performance. Materials and Methods: Dose kernels corresponding to different energy and source configurations were calculated using MCNPX in phantom and voxelized patient CT scans, and then converted to biological equivalent dose using depth dependent RBE weighting factors derived from theory and experiment. Linear equations were formulated for each pixel representing superposition of different kernels weighted by unknown intensities. Algorithms using constrained least square and gradient descent optimization were developed to minimize objective functions measuring the geometric correlation of the planning target volume (PTV) with the calculated distribution, yielding an optimized intensity for beams as function of energy and direction. Results: Biologically optimized treatment plans implemented on a voxelized 38 year old human were in good agreement with the input PTVs, reproducing the PTVs with a mean error of less than 2.24%. Proof of principle demonstrations were successful in producing complicated structures, such resemblance of Einstein, in water phantom with a correlation greater than 93%. Conclusions: We have developed a Monte Carlo treatment planning system for energy and intensity modulated antiproton therapy capable of incorporating depth‐dependency of the RBE, and reproducing complicated PTVs with high accuracy. The work can be readily extended to incorporate more sophisticated objective functions such as NTCP and TCP functionals. AU - Fahimian, B.* AU - Demarco, J.* AU - Keyes, R.* AU - Luan, S.* AU - Zankl, M. AU - Holzscheiter, M.* C1 - 51609 C2 - 0 SP - 2758-2759 TI - WE‐C‐BRB‐06: Antiproton Radiotherapy: Development of Physically and Biologically Optimized Monte Carlo Treatment Planning Systems for Intensity and Energy Modulated Delivery. JO - Med. Phys. VL - 36 IS - 6 PY - 2009 SN - 0094-2405 ER - TY - JOUR AB - Optoacoustic imaging is emerging as a noninvasive imaging modality that can resolve optical contrast through several millimeters to centimeters of tissue with the resolution achieved by ultrasound imaging. More recently, applied at multiple illumination wavelengths, multispectral optoacoustic tomography (MSOT) offered the ability to effectively visualize tissue biomarkers by resolving their distinct spectral signatures. While the imaging potential of the method has been demonstrated, little is known on the sensitivity performance in resolving chromophoric and fluorescent substances, such as optical functional and molecular reporters. Herein the authors investigate the detection capacity and physical limits of tomographic optoacoustic imaging by simulating signals originating from absorbing spheres in tissue-mimicking media. To achieve this, a modified optoacoustic equation is employed to incorporate wavelength-dependent propagation and attenuation of diffuse light and ultrasound. The theoretical predictions are further validated in phantom experiments involving Cy5.5, a common near-infrared fluorescent molecular agent. AU - Razansky, D. AU - Baeten, J. AU - Ntziachristos, V. C1 - 2248 C2 - 26195 SP - 939-945 TI - Sensitivity of molecular target detection by multispectral optoacoustic tomography (MSOT). JO - Med. Phys. VL - 36 IS - 3 PB - Amer Assoc Physicists Medicine Amer Inst Physics PY - 2009 SN - 0094-2405 ER - TY - JOUR AB - PURPOSE: Previous work has demonstrated that there are significant dose variations with a sinusoidal pattern on the peripheral of a CTDI 32 cm phantom or on the surface of an anthropomorphic phantom when helical CT scanning is performed, resulting in the creation of "hot" spots or "cold" spots. The purpose of this work was to perform preliminary investigations into the feasibility of exploiting these variations to reduce dose to selected radiosensitive organs solely by varying the tube start angle in CT scans. METHODS: Radiation dose to several radiosensitive organs (including breasts, thyroid, uterus, gonads, and eye lenses) resulting from MDCT scans were estimated using Monte Carlo simulation methods on voxelized patient models, including GSF's Baby, Child, and Irene. Dose to fetus was also estimated using four pregnant female models based on CT images of the pregnant patients. Whole-body scans were simulated using 120 kVp, 300 mAs, both 28.8 and 40 mm nominal collimations, and pitch values of 1.5, 1.0, and 0.75 under a wide range of start angles (0 degree-340 degrees in 20 degrees increments). The relationship between tube start angle and organ dose was examined for each organ, and the potential dose reduction was calculated. RESULTS: Some organs exhibit a strong dose variation, depending on the tube start angle. For small peripheral organs (e.g., the eye lenses of the Baby phantom at pitch 1.5 with 40 mm collimation), the minimum dose can be 41% lower than the maximum dose, depending on the tube start angle. In general, larger dose reductions occur for smaller peripheral organs in smaller patients when wider collimation is used. Pitch 1.5 and pitch 0.75 have different mechanisms of dose reduction. For pitch 1.5 scans, the dose is usually lowest when the tube start angle is such that the x-ray tube is posterior to the patient when it passes the longitudinal location of the organ. For pitch 0.75 scans, the dose is lowest when the tube start angle is such that the x-ray tube is anterior to the patient when it passes the longitudinal location of the organ. CONCLUSIONS: Helical MDCT scanning at pitch 1.5 and pitch 0.75 results in "cold spots" and "hot spots" that are created both at surface and in-depth locations within patients. For organs that have a relatively small longitudinal extent, dose can vary considerably with different start angles. While current MDCT systems do not provide the user with the ability to control the tube start angle, these results indicate that in these specific situations (pitch 1.5 or pitch 0.75, small organs and especially small patients), there could be significant dose savings to organs if that functionality would be provided. AU - Zhang, D.* AU - Zankl, M. AU - DeMarco, J.J.* AU - Cagnon, C.H.* AU - Angel, E.* AU - Turner, A.C.* AU - McNitt-Gray, M.F.* C1 - 534 C2 - 27318 SP - 5654-5664 TI - Reducing radiation dose to selected organs by selecting the tube start angle in MDCT helical scans: A Monte Carlo based study. JO - Med. Phys. VL - 36 IS - 12 PB - American Assoc. of Physicists in Medicine PY - 2009 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Previous work demonstrated that there are significant dose variations on the peripheral, or surface of either a CTDI 32cm phantom or an anthropomorphic phantom when helical CT scanning is performed. The purpose of this work is to investigate the effectiveness of exploiting these variations to reduce dose to targeted radiosensitive organs solely by varying the tube start angle in CT scans. Method and Materials: Radiation dose to several radiosensitive organs (including breasts, thyroid, uterus, gonads, lens of eyes) from a MDCT CT scanner were estimated using Monte Carlo simulation methods on GSF Baby phantom. Whole body scans were simulated using 120kVp, 300mAs, 28.8 mm nominal collimation, pitch 1.5 under a wide range of start angles (0 to 340 degrees in 20 degree increments). The relationship between tube start angle and organ dose was examined for each organ and the potential dose reduction was calculated. Results: The organ dose shows obvious variation depending on the tube start angle. For small peripheral organs, (e.g. the lens of eyes), the minimum dose can be 35% lower than the maximum dose, depending on tube start angle. For pitch 1.5 scans, the dose is usually lowest when the tube start angle is such that the x‐ray tube is posterior to the patient when it passes the longitudinal location of the organ. Conclusion: Helical MDCT scanning results in “cold spots” and “hot spots” that are created both at surface and even in‐depth locations within patients. If organs have a relatively small longitudinal extent, their dose may be reduced by selecting the tube start angle such that the location of these “cold spots” may be manipulated by appropriately selecting the tube start angle. This dose reduction should not have any implications for image quality as there is no change in mAs or total mAs. AU - Zhang, D.* AU - Demarco, J.* AU - Cagnon, C.* AU - Angel, E.* AU - Turner, A.* AU - Zankl, M. AU - Mcnitt‐gray, M.* C1 - 51611 C2 - 0 SP - 2728 TI - TU‐C‐304A‐06: Reducing Dose to a Small Organ by Varying the Tube Start Angle in a Helical CT Scan. JO - Med. Phys. VL - 36 IS - 6 PY - 2009 SN - 0094-2405 ER - TY - JOUR AB - Purpose: Recent in vitro experiments at CERN have demonstrated a superior biological effectiveness for antiprotons relative to protons. A continued concern is the normal tissue dose resulting from annihilation neutrons. Using Monte Carlo simulations of a CT‐based anthropomorphic human phantom, we quantify the physical dose from annihilation byproducts and present the first organ specific calculations of normal tissue equivalent dose from neutrons in antiproton therapy. Method and Materials: MCNPX and FLUKA were utilized to model antiproton irradiation of the segmented whole‐body phantom of a 38 year old male representing the ICRP reference man. The fluence was tallied as a function of energy and organ type for a 75 MeV antiproton pencil beam with a Bragg peak located in the frontal lobe of the phantom's brain. Physical dose was calculated for each organ as a function of energy using fluence to kerma conversion coefficients (ICRU‐63). Finally, using energy dependent radiation weighting factors (ICRP‐60), the equivalent dose from neutrons was estimated for each organ. Results: The results indicate a neutron fluence on the order of 10 −5 cm −2 per incident antiproton for the bladder and colon, and a neutron fluence on the order of 10 −4 cm −2 per incident antiproton for the thyroid and esophagus. As anticipated, the physical and equivalent doses are dependent on the irradiation geometry and the proximity of the organs to the Bragg peak; of the organs tallied, bone and thyroid received the highest physical and equivalent dose for the given irradiation protocol. The estimates of organ physical and equivalent dose and their uncertainties are discussed. Conclusion: We have developed an anthropomorphic Monte Carlo model for antiproton therapy. The model provides a method for more sophisticated biological modeling of treatment response such as cost basis analysis of TCP and NTCP relative to other treatment modalities. AU - Fahimian, B.* AU - Demarco, J.* AU - Holzscheiter, M.* AU - Keyes, R.* AU - Bassler, N.* AU - Iwamoto, K.* AU - Zankl, M. C1 - 51610 C2 - 0 SP - 2874 TI - MO‐E‐AUD B‐02: Antiproton Therapy: Monte Carlo Simulations of Normal Tissue Equivalent Dose From Annihilation Neutrons. JO - Med. Phys. VL - 35 IS - 6 PY - 2008 SN - 0094-2405 ER - TY - JOUR AB - The shielding properties of two different lead-free materials-tin and a compound of 80% tin and 20% bismuth-for protective clothing are compared with those of lead for three typical x-ray spectra generated at tube voltages of 60, 75, and 120 kV. Three different quantities were used to compare the shielding capability of the different materials: (1) Air-kerma attenuation factors in narrow-beam geometry, (2) air-kerma attenuation factors in broad-beam geometry, and (3) ratios of organ and effective doses in the human body for a whole-body irradiation with a parallel beam directed frontally at the body. The thicknesses of tin (0.45 mm) and the tin/bismuth compound (0.41 mm) to be compared against lead correspond to a lead equivalence value of 0.35 mm for the 75 kV spectrum. The narrow-beam attenuation factors for 0.45 mm tin are 54% and 32% lower than those for 0.35 mm lead for 60 and 120 kV; those for 0.41 mm tin/bismuth are 12% and 32% lower, respectively. The decrease of the broad-beam air-kerma attenuation factors compared to lead is 74%, 46%, and 41% for tin and 42%, 26%, and 33% for tin/bismuth and the spectra at 60, 75, and 120 kV, respectively. Therefore, it is recommended that the characterization of the shielding potential of a material should be done by measurements in broad-beam geometry. Since the secondary radiation that is mainly responsible for the shielding reduction in broad-beam geometry is of low penetrability, only more superficially located organs receive significantly enhanced doses. The increase for the dose to the glandular breast tissue (female) compared to being shielded by lead is 143%, 37%, and 45% when shielded by tin, and 35%, 15%, and 39% when shielded by tin/bismuth for 60, 75, and 120 kV, respectively. The effective dose rises by 60%, 6%, and 38% for tin, and 14%, 3% and, 35% for tin/bismuth shielding, respectively. AU - Schlattl, H. AU - Zankl, M. AU - Hoeschen, C. C1 - 4770 C2 - 25048 SP - 4270-4280 TI - Shielding properties of lead-free protective clothing and their impact on radiation doses. JO - Med. Phys. VL - 34 IS - 11 PB - AAPM PY - 2007 SN - 0094-2405 ER - TY - JOUR AB - A methodology for ferrokinetic studies based on the administration of iron stable isotopes was developed. Fractional plasma clearance and intestinal iron absorption in rabbits were determined using the double tracer technique. Three rabbits were given 5 8Fe solution intravenously and about 40 min later 5 7Fe solution orally. Blood samples were drawn at different times following administration. The analysis of the single iron isotopes content in plasma samples was made by proton nuclear activation. The results were compared with those obtained from the administration, to the same rabbits, of the radioactive isotopes 5 5Fe and 5 9Fe. The agreement was found to be satisfactory. AU - Werner, E. AU - Cantoue, M.C. AU - Molha, N. AU - Pirolla, L. AU - Hansen, Ch. AU - Roth, P. C1 - 17320 C2 - 10043 SP - 223-227 TI - Ferrocinetic Studies with Stable Isotopes as Tracers. JO - Med. Phys. VL - 14 IS - 2 PY - 1987 SN - 0094-2405 ER -