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Trinkl, S. ; Tessonnier, T.* ; Mares, V. ; Dommert, M. ; Wielunski, M. ; Wilkens, J.J.* ; Parodi, K.* ; Rühm, W.

Secondary neutron spectra and ambient dose equivalent measurements with an extended range Bonner sphere spectrometer in clinical pencil beam scanning using protons, helium, carbon, and oxygen ions.

Phys. Med. Biol. 71:015034 (2026)
Postprint DOI PMC
Open Access Green
Particle therapy is an advanced radiotherapy technique primarily using protons and carbon ions, with helium and oxygen ions also being considered for clinical applications. A critical concern in ion therapy is the production of secondary neutrons due to nuclear reactions, which may contribute to unwanted dose deposition within the patient. Approach: This study investigates neutron production for different ion species and energies, providing essential data for assessing secondary neutron exposure. Protons, helium, carbon, and oxygen ions were used to irradiate a PMMA phantom at two energies, corresponding to penetration depths of approximately 5 cm and 14 cm in water. The secondary neutron fluence and ambient dose equivalent (H*(10)) were measured using an extended-range Bonner sphere spectrometer at four angular positions (0°, 45°, 90°, and 135°) relative to the beam direction. Main results: Results showed significant differences in neutron production depending on ion species and energy. The neutron ambient dose equivalent per primary ion in the beam direction varied by a factor of about 50 across the different ion species. When normalized to the absorbed dose in the pristine Bragg peak, variations of up to a factor of 10 were observed between proton and oxygen ions. However, at off-axis positions, neutron ambient dose equivalent per absorbed dose was relatively similar across ion species, even lower for ions heavier than protons when normalizing to the biologically effective treatment dose. Significance: This study presents the first measurement-based comparative analysis of fluence energy distributions and neutron equivalent doses for protons, helium, carbon, and oxygen ions in a synchrotron-based clinical facility for monoenergetic beams. These findings are highly relevant for evaluating secondary neutron exposure in particle therapy and optimizing treatment strategies to reduce long term-risks of radiation induced second cancers. .
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Publication type Article: Journal article
Document type Scientific Article
Keywords Neutron Spectrometry ; Neutron Dose ; Carbon Ions ; Helium Ions ; Oxygen Ions ; Protons; Pediatric-patients; Particle Therapy; Monte-carlo; Radiation; Field; Risk; Radiotherapy; Dosimetry; Facility; Tumors
ISSN (print) / ISBN 0031-9155
e-ISSN 1361-6560
Journal Physics in Medicine and Biology
Quellenangaben Volume: 71, Issue: 1, Pages: , Article Number: 015034 Supplement: ,
Publisher Institute of Physics Publishing (IOP)
Publishing Place Bristol
Reviewing status Peer reviewed
Institute(s) Institute of Radiation Protection (ISS)
Grants Deutsche Forschungsgemeinschaft