Secondary radiation damage caused by proton radiation therapy can affect other tissues and result in unwanted doses. Therefore, it is necessary to calculate the secondary radiation doses (from scattering processes) for radiation protection issues. In this study, we simulated a proton beam in a 10 cm distance (from source-to-surface distance) was used to irradiate a hypothetical breast tumor at the MIRD phantom under conditions of variable beam radius and energy. Thereafter, absorbed doses to the tumor and scattering radiation doses to the heart, lung, liver, stomach, and spleen were calculated. The results showed that the maximum scattered neutron dose-to-organs close to the breast, such as the heart, lung, liver, stomach and spleen, with 70 MeV proton energy and beam radius of 1 cm are negligible. Finally, the spread-out Bragg peak was obtained using an appropriate weighted combination of beams of different energies which can be replaced as a suitable method instead of modulator wheel design for applying in MCNPX code input program.

The evaluated indices in this study are the absorbed tumor doses for single particle and the scattered doses due neutrons and photons. The results showed that the majority of scattered radiation is neutrons. Scattered particle spectral powers for neutrons and photons were also plotted. It was observed that in the photon spectra, the maximum scattered radiation occurs with the beam of 1 cm radius and 70 MeV energy, while the neutron spectra show that scattered radiation is predominantly at low energy. Finally, a spread-out Bragg peak appropriate for a hypothetical tumor with 1.77 cm width was obtained, and the absorbed doses and scattered doses were calculated.

质子放射疗法引起的继发性放射损伤会影响其他组织，并导致不必要的剂量。因此，有必要针对辐射防护问题计算二次辐射剂量（来自散射过程）。在这项研究中，我们模拟了一个10 cm距离（从源到表面的距离）的质子束，用于在可变束半径和能量的条件下，在MIRD体模上照射假想的乳腺肿瘤。此后，计算对肿瘤的吸收剂量和对心脏，肺，肝，胃和脾的散射辐射剂量。结果表明，具有70 MeV质子能和1 cm束半径的靠近乳房的最大散射中子剂量对器官，如心脏，肺，肝，胃和脾脏，可以忽略不计。最后，

在这项研究中评估的指标是单个粒子的吸收肿瘤剂量以及中子和光子引起的散射剂量。结果表明，大部分散射辐射是中子。还绘制了中子和光子的散射粒子光谱功率。观察到，在光子光谱中，最大散射辐射发生在半径为1 cm且能量为70 MeV的光束中，而中子光谱表明，散射辐射主要处于低能量状态。最终，获得了适用于假设的肿瘤，其宽度为1.77 cm的散布的Bragg峰，并计算了吸收剂量和分散剂量。