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Phys Med Biol. 2018 Dec 18;63(24):245021. doi: 10.1088/1361-6560/aaf34a.
The change in optical properties of GafChromic films depends not only on the absorbed dose, but also on the linear energy transfer (LET) of the ionizing radiation. The influence of LET on the film dose-response relationship is especially important when films are applied for dosimetry of energetic charged particles. In the present study, we examined the response of the unlaminated EBT3 and MD-V3 films to proton, deuterium and helium beams with energies in the range of several megaelectronvolts (MeV). Films were exposed to doses up to 200 Gy and a model based on the bimolecular chemical reaction was chosen to fit the measured film signals. The LET in the active layers of the films and the dose correction factors were computed with Monte Carlo software TRIM. Signal quenching, observed for all ion beams in comparison to x-rays, was investigated as a function of the LET in the range of 10-100 keV µm. The response of the films got weaker with increasing the LET and showed no dependence on the ion species. The LET effect was quantified by introducing a modified expression for the relative effectiveness (RE) by which a unique RE value is assigned to a single LET. The RE defined in that way decreased from about 90% for LET of 10 keV µm to less than 50% for LET of 100 keV µm. Similar behavior was observed for EBT3 and MD-V3 film models.
GafChromic 薄膜的光学性质变化不仅取决于吸收剂量，还取决于电离辐射的线性能量传递 (LET)。当薄膜用于测量高能带电粒子的剂量时，LET 对薄膜剂量响应关系的影响尤为重要。在本研究中，我们研究了未层压的 EBT3 和 MD-V3 薄膜对能量在数兆电子伏特 (MeV) 范围内的质子、氘和氦束的响应。薄膜的照射剂量高达 200 Gy，选择基于双分子化学反应的模型来拟合测量的薄膜信号。使用蒙特卡罗软件 TRIM 计算了薄膜活性层中的 LET 和剂量修正因子。与 X 射线相比，所有离子束都观察到信号猝灭，研究了其与 LET 之间的关系（LET 在 10-100 keV µm 范围内）。随着 LET 的增加，薄膜的响应变弱，且与离子种类无关。通过引入相对有效性 (RE) 的修正表达式来量化 LET 效应，该表达式为单个 LET 分配了唯一的 RE 值。以这种方式定义的 RE 值从 LET 为 10 keV µm 时的约 90%下降到 LET 为 100 keV µm 时的小于 50%。EBT3 和 MD-V3 薄膜模型也表现出类似的行为。
