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Measurement of stray radiation in scanning proton radiotherapy- Summary of the EURADOS WG 9 intercomparison results with passive and active dosimetry systems

Proton beam therapy has advantages in comparison to conventional photon radiotherapy due to the physical properties of proton beams. However, the interactions of protons with matter result in the production of secondary radiation, comprised mostly of neutrons and gamma radiation. This component may lead to unwanted out-of-field doses deposited distantly from the target volume and consequently an increased probability of late effects such as secondary cancers. The EURADOS Working Group 9 (Radiation dosimetry in radiotherapy) Sub Group 2 (Hadron therapy) performed comprehensive measurements of out-of-field neutron and photon doses inside a water phantom irradiated in the IBA (230 MeV) active-scanning proton beam therapy facility in Trento, Italy. 3-D mapping of out-of-field doses generated by a therapeutic proton pencil scanning beam (PBS) in a 300 × 300 × 600 mm3 water phantom was performed using different types of thermoluminescence detectors (MTS-7, MTS-6, MTS-N, TLD-700), radiophotoluminescent detectors (GD-352M and GD-302M) and track-etched detectors (PADAC). Neutron and gamma-ray doses were experimentally determined at 200 points within the phantom. In parallel, GEANT 4 Monte Carlo code was applied to calculate neutron and gamma radiation spectra at the position of each detector. The second part of the measurement campaign was focused on measuring and testing different commercially available active dosimetry systems (Bonner sphere systems, TEPCs (Hawk) and proportional counters) for measurements of secondary radiation generated by a PBS. Measurements of neutron ambient dose equivalents, H*(10), were performed at several positions inside and outside the treatment room whilst irradiating the water phantom. An overview of the selected final results of stray radiation in proton therapy measured with active and passive detectors will be presented.

scanning proton radiotherapy ; stray radiation ; passive detectors ; active detectors ; EURADOS

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