Shimo Takahiro, Shiba Shintaro, Watanabe Hiroyuki, Yamanaka Masashi, Matsumoto Kazuki, Yamano Akihiro, Tokuuye Kohichi
Department of Radiological Science, Showa University Graduate School of Health Sciences, Shinagawa-ku, Tokyo, Japan.
Department of Medical Physics, Shonan Kamakura General Hospital, Kamakura City, Japan.
J Med Phys. 2025 Jan-Mar;50(1):14-19. doi: 10.4103/jmp.jmp_206_24. Epub 2025 Mar 24.
This study evaluated whether the mini-ridge filter (MRF) used for beam energy optimization in a synchrotron-based proton beam therapy (PBT) affects the generation of secondary neutrons and photons.
Secondary radiation from the PBT was evaluated using a Monte Carlo simulation (MCS) with the Particle and Heavy-ion Transport code System (version 3.31), and the PROBEAT-M1 system (Hitachi, Japan) was modeled. In the analysis, we focused on the production of neutrons and photons in a 35 cm ×35 cm ×35 cm water phantom with and without MRF to ensure the accuracy of the dose calculation.
The MCS results were in good agreement with the measurement results, and the off-axis ratio at the center of the spread-out Bragg peak was 100% at a gamma analysis pass rate of 2 mm/2%. The photon fluence decreased by 4.0 and 0.9% at 70.2 and 228.7 MeV, respectively, but no significant effect on total neutron and photon production was observed ( > 0.05). The MRF effect on the dose was <0.11 μGy Gy, suggesting that a clinically significant effect is negligible.
These results demonstrated that MRF had a limited effect on the generation of secondary radiation in PBT. MRF, which is used to improve dose distribution, has the potential to be safely used without increasing secondary radiation, and MRF might not affected to generate secondary radiation to clinically meaningful levels.
本研究评估了用于基于同步加速器的质子束治疗（PBT）中束流能量优化的微型脊形滤波器（MRF）是否会影响次级中子和光子的产生。
使用粒子与重离子传输代码系统（版本3.31）的蒙特卡罗模拟（MCS）评估PBT的次级辐射，并对PROBEAT-M1系统（日本日立公司）进行建模。在分析中，我们重点关注在有和没有MRF的35 cm×35 cm×35 cm水模体中中子和光子的产生情况，以确保剂量计算的准确性。
MCS结果与测量结果高度吻合，在2 mm/2%的伽马分析通过率下，扩展布拉格峰中心的离轴比为100%。在70.2和228.7 MeV时，光子注量分别下降了4.0%和0.9%，但未观察到对总中子和光子产生有显著影响（P>0.05）。MRF对剂量的影响<0.11 μGy/Gy，表明临床上显著的影响可忽略不计。
这些结果表明，MRF对PBT中次级辐射的产生影响有限。用于改善剂量分布的MRF有潜力在不增加次级辐射的情况下安全使用，并且MRF可能不会将次级辐射产生到具有临床意义的水平。
