Grupo de Física Nuclear, EMFTEL and IPARCOS, Universidad Complutense de Madrid, CEI Moncloa, Madrid, Spain.
Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Madrid, Spain.
Phys Med Biol. 2021 May 20;66(11). doi: 10.1088/1361-6560/abfc8d.
Passive dosimetry with radiochromic films is widely used in proton radiotherapy, both in clinical and scientific environments, thanks to its simplicity, high spatial resolution and dose-rate independence. However, film under-response for low-energy protons, the so-called linear-energy transfer (LET) quenching, must be accounted and corrected for. We perform a meta-analysis on existing film under-response data with EBT, EBT2 and EBT3 GAFchromic™ films and provide a common framework to integrate it, based on the calculation of dose-averaged LET in the active layer of the films. We also report on direct measurements with the 10 MeV proton beam at the Center for Microanalysis of Materials (CMAM) for EBT2, EBT3 and unlaminated EBT3 films, focusing on the 20-80 keVmLET range, where previous data was scarce. Measured film relative efficiency (RE) values are in agreement with previously reported data from the literature. A model on film RE constructed with combined literature and own experimental values in the 5-80 keVmLET range is presented, supporting the hypothesis of a linear decrease of RE with LET, with no remarkable differences between the three types of films analyzed.
放射色迹胶片的被动剂量测定在质子放射治疗中得到了广泛应用，无论是在临床环境还是科学环境中，这都要归功于其简单性、高空间分辨率和剂量率独立性。然而，对于低能量质子，必须考虑并校正胶片的低响应，即所谓的线性能量转移（LET）淬灭。我们对现有的 EBT、EBT2 和 EBT3 GAFchromic™ 胶片的胶片低响应数据进行了荟萃分析，并基于胶片活性层中的平均剂量 LET 的计算，为其提供了一个通用的整合框架。我们还报告了在材料微分析中心（CMAM）的 10 MeV 质子束下对 EBT2、EBT3 和未层压 EBT3 胶片进行的直接测量，重点关注 20-80 keVmLET 范围，因为之前的数据很少。测量得到的胶片相对效率（RE）值与文献中之前报道的数据一致。在 5-80 keVmLET 范围内，我们提出了一个基于文献和我们自己的实验值的胶片 RE 模型，该模型支持 RE 随 LET 线性下降的假设，三种分析的胶片之间没有明显差异。
