Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, 30013 Taiwan.
Phys Med Biol. 2013 Mar 7;58(5):1391-413. doi: 10.1088/0031-9155/58/5/1391. Epub 2013 Feb 11.
Neutron and gamma-ray mixed field dosimetry remains one of the most challenging topics in radiation dosimetry studies. However, the requirement for accurate mixed field dosimetry is increasing because of the considerable interest in high-energy radiotherapy machines, medical ion beams and BNCT epithermal neutron beams. Therefore, this study investigated the GafChromic® EBT2 film. The linearity, reproducibility, energy dependence and homogeneity of the film were tested in a (60)Co medical beam, 6-MV LINAC and 10-MV LINAC. The linearity and self-developing effect of the film irradiated in an epithermal neutron beam were also examined. These basic detector characteristics showed that EBT2 film can be effectively applied in mixed field dosimetry. A general detector response model was developed to determine the neutron relative effectiveness (RE) values. The RE value of fast neutrons varies with neutron spectra. By contrast, the RE value of thermal neutrons was determined as a constant; it is only 32.5% in relation to gamma rays. No synergy effect was observed in this study. The lithium-6 capture reaction dominates the neutron response in the thermal neutron energy range, and the recoil hydrogen dose becomes the dominant component in the fast neutron energy region. Based on this study, the application of the EBT2 film in the neutron and gamma-ray mixed field is feasible.
中子和伽马混合场剂量学仍然是辐射剂量学研究中最具挑战性的课题之一。然而，由于对高能放射治疗机、医用离子束和硼中子俘获治疗（BNCT）超热中子束的极大兴趣，对精确的混合场剂量学的要求正在不断提高。因此，本研究调查了 GafChromic® EBT2 胶片。在（60）Co 医用射束、6MV LINAC 和 10MV LINAC 中测试了胶片的线性度、再现性、能量依赖性和均匀性。还检查了在超热中子射束中辐照的胶片的线性度和自显影效应。这些基本的探测器特性表明，EBT2 胶片可以有效地应用于混合场剂量学。开发了一个通用的探测器响应模型来确定中子相对有效性（RE）值。快中子的 RE 值随中子能谱而变化。相比之下，热中子的 RE 值被确定为常数，相对于伽马射线仅为 32.5%。在本研究中没有观察到协同效应。在热中子能量范围内，锂-6 俘获反应主导着中子响应，而反冲氢剂量成为快中子能量区域的主要组成部分。基于本研究，EBT2 胶片在中子和伽马射线混合场中的应用是可行的。
