应用Geant4模拟EBT3胶片的能量响应和质子射程测量

目的 计算EBT3胶片吸收剂量的能量依赖性，展示EBT3胶片测量质子吸收剂量时的误差。方法 在临床光子和质子能量照射范围内逐步增加射线束能量，应用Geant4计算EBT3胶片吸收剂量与同体积水吸收剂量的差异，并与理论结果进行比对。结果 对于光子和质子来说，EBT3胶片吸收剂量能量依赖性与理论结果一致的分界线分别为100 keV和11 MeV；光子和质子能量高于相应值时EBT3胶片能量依赖性与理论结果保持一致，低于相应值时EBT3胶片能量依赖性与理论结果无关；计算EBT3胶片测量质子布拉格峰和50%剂量点与实际位置的差异，最大误差小于1%。结论 对较高能量区间内的质子和光子来说，EBT3胶片吸收剂量能量依赖性可忽略；对低能量区间的质子和光子，EBT3胶片吸收剂量能量依赖性差异较大，应给予重点关注。EBT3胶片测量的质子布拉格峰和50%剂量点与实际位置基本一致。

Energy response and proton range measurement with EBT3 film simulated by Geant4

Objective To calculate the energy dependence of absorbed dose in EBT3 film, and to reveal the error in the measurement of proton absorbed dose by EBT3 film. Methods Beam energy was gradually increased in the clinical photon and proton energy ranges. Geant4 was used to calculate the difference in absorbed dose between EBT3 film and the same volume of water. The results were compared with the theoretical values. Results For photons and protons, the thresholds for absorbed dose with energy dependence were 100 keV and 11 MeV, respectively. The energy dependence was consistent with the theoretical values when the photon and proton energies were higher than the corresponding thresholds, and irrelevant to the theoretical values when energies were lower than the thresholds. The differences between the proton Bragg peak and 50% dose point and the actual positions were less than 1%. Conclusions For protons and photons with high energy, the energy dependence of absorbed dose in EBT3 film is negligible. For protons and photons with low energy, EBT3 film shows very different energy dependence of absorbed dose, which should be taken into consideration. The proton Bragg peak and 50% dose point measured by EBT3 film are basically the same as the actual positions.