Clements Nathan, Bazalova-Carter Magdalena
Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada.
J Appl Clin Med Phys. 2024 Dec;25(12):e14529. doi: 10.1002/acm2.14529. Epub 2024 Sep 13.
To use Monte Carlo simulations to study the absorbed-dose energy dependence of GAFChromic EBT3 and EBT4 films for 5-200 MeV electron beams and 100 keV-15 MeV photon beams considering two film compositions: a previous EBT3 composition (Bekerat et al.) and the final composition of EBT3/current composition of EBT4 (Palmer et al.).
A water phantom was simulated with films at 5-50 mm depth in 5 mm intervals. The water phantom was irradiated with flat, monoenergetic 5-200 MeV electron beams and 100 and 150 keV kilovoltage and 1-15 MeV megavoltage photon beams and the dose to the active layer of the films was scored. Simulations were rerun with the films defined as water to compare the absorbed-dose response of film to water, .
For electrons, the Bekerat et al. composition had variations in of up to from 5 to 200 MeV. Similarly, the Palmer et al. composition had differences in up to from 5 to 200 MeV. For photons, varied up to and from 100 keV to 15 MeV for the Bekerat et al. and Palmer et al. compositions, respectively. The depth of films did not appear to significantly affect for photons at any energy and for electrons at energies 50 MeV. However, for 5 and 10 MeV electrons, decreases of up to in were seen due to stacked films and increased beam attenuation in films compared to water.
The up to and variations in for electrons and photons, respectively, across the energies considered in this study indicate the importance of calibrating films with the energy intended for measurement. Additionally, this work emphasizes potential issues with stacking films to measure depth dose curves, particularly for electron beams with energies 10 MeV.
使用蒙特卡罗模拟研究考虑两种薄膜成分的GAFChromic EBT3和EBT4薄膜对于5 - 200 MeV电子束以及100 keV - 15 MeV光子束的吸收剂量能量依赖性，这两种成分分别是之前的EBT3成分（贝克拉特等人）以及EBT3的最终成分/EBT4的当前成分（帕尔默等人）。
模拟了一个水模体，薄膜位于深度为5 - 50 mm处，间隔为5 mm。用水模体接受能量分别为5 - 200 MeV的平面单能电子束、100 keV和150 keV的千伏级以及1 - 15 MeV的兆伏级光子束照射，并对薄膜活性层的剂量进行评分。将薄膜定义为水重新进行模拟，以比较薄膜与水的吸收剂量响应。
对于电子束，贝克拉特等人的成分在5至200 MeV范围内的变化高达 。同样，帕尔默等人的成分在5至200 MeV范围内的差异高达 。对于光子束，贝克拉特等人和帕尔默等人的成分在100 keV至15 MeV范围内的 变化分别高达 和 。薄膜深度对于任何能量的光子以及能量 50 MeV的电子的 似乎没有显著影响。然而，对于5 MeV和10 MeV的电子，与水相比，由于薄膜堆叠和薄膜中束衰减增加， 最多降低了 。
在本研究考虑的能量范围内，电子和光子的 分别高达 和 的变化表明使用预期测量能量对薄膜进行校准的重要性。此外，这项工作强调了堆叠薄膜测量深度剂量曲线时的潜在问题，特别是对于能量 10 MeV的电子束。
