Speaker
Description
Proton therapy provides superior dose conformity compared to conventional photon techniques. However, nuclear interactions of therapeutic proton beams generate secondary radiation, particularly neutrons, contributing to out-of-field dose. Although generally low, accurate quantification of these doses is essential for risk assessment, radiation protection optimization, and validation of computational models. This study investigates secondary neutron dose during proton head irradiation under clinically relevant conditions. The results support Monte Carlo validation and improve patient-specific risk estimation, particularly for sensitive groups such as pediatric and pregnant patients, where fetal dose assessment is crucial for treatment planning.
Experimental measurements were performed using an anthropomorphic phantom in a head-irradiation setup. Calibrated neutron REM counters (Wendi-II) were positioned at two locations outside the primary field. Measurements covered a range of delivered doses to assess detector reproducibility and response for varying spill lengths. Additional tests evaluated the influence of detector distance from the isocenter and treatment room environment. Monte Carlo simulations were conducted to aid data interpretation and estimate correction factors accounting for detector response.
Ambient dose equivalent measurements showed high consistency with increasing incident protons per spill. The Wendi-II detector demonstrated stable, reproducible performance, yielding 2.47 µSv/Gy at the abdomen position and 8.15 ± 0.02 µSv/Gy above the head. Measurements in different rooms produced comparable results (2.47 vs. 2.38 µSv/Gy and 8.15 vs. 7.50 µSv/Gy), indicating minimal influence of the surroundings. A clear reduction in neutron dose was observed with increasing distance from the isocenter. Monte Carlo simulations reproduced overall trends, though quantitative differences reflected detector and modeling sensitivities.
This study systematically evaluates secondary neutron dose during proton head irradiation. The findings confirm reliable neutron dose measurements in clinical proton therapy and highlight spatial factors in dose assessment. The combined experimental and simulation approach enhances secondary radiation characterization, model validation, and radiation protection in proton therapy.