Department of Radiation Oncology, McLaren Regional Medical Center, Flint, MI 48532, USA.
Med Phys. 2012 Feb;39(2):912-21. doi: 10.1118/1.3678989.
One of the fundamental parameters used for dose calculation is percentage depth-dose, generally measured employing ionization chambers. There are situations where use of ion chambers for measuring depth-doses is difficult or problematic. In such cases, radiochromic film might be an alternative. The EBT-2 model GAFCHROMIC™ film was investigated as a potential tool for depth-dose measurement in radiotherapy beams over a broad range of energies and modalities.
Pieces of the EBT-2 model GAFCHROMIC™ EBT2 film were exposed to x-ray, electron, and proton beams used in radiotherapy. The beams employed for this study included kilovoltage x-rays (75 kVp), (60)Co gamma-rays, megavoltage x-rays (18 MV), electrons (7 and 20 MeV), and pristine Bragg-peak proton beams (126 and 152 MeV). At each beam quality, film response was measured over the dose range of 0.4-8.0 Gy, which corresponds to optical densities ranging from 0.05 to 0.4 measured with a flat-bed document scanner. To assess precision in depth-dose measurements with the EBT-2 model GAFCHROMIC™ film, uncertainty in measured optical density was investigated with respect to variation in film-to-film and scanner-bed uniformity.
For most beams, percentage depth-doses measured with the EBT-2 model GAFCHROMIC™ film show an excellent agreement with those measured with ion chambers. Some discrepancies are observed in case of (i) kilovoltage x-rays at larger depths due to beam-hardening, and (ii) proton beams around Bragg-peak due to quenching effects. For these beams, an empirical polynomial correction produces better agreement with ion-chamber data.
The EBT-2 model GAFCHROMIC™ film is an excellent secondary dosimeter for measurement of percentage depth-doses for a broad range of beam qualities and modalities used in radiotherapy. It offers an easy and efficient way to measure beam depth-dose data with a high spatial resolution.
剂量计算中使用的基本参数之一是百分深度剂量，通常使用电离室进行测量。在某些情况下，使用电离室测量深度剂量会比较困难或存在问题。在这种情况下，可能会选择使用光致变色胶片。EBT-2 型 GAFCHROMIC™胶片被研究作为一种在广泛的能量和模式范围内用于放射治疗光束的深度剂量测量的潜在工具。
EBT-2 型 GAFCHROMIC™ EBT2 胶片的一些部分暴露于放射治疗中使用的 X 射线、电子和质子束。为了进行这项研究，使用了千伏 X 射线（75 kVp）、（60）Co 伽马射线、兆伏 X 射线（18 MV）、电子（7 和 20 MeV）以及原始布拉格峰质子束（126 和 152 MeV）。在每种射线质量下，在 0.4-8.0 Gy 的剂量范围内测量胶片的响应，这对应于使用平板文档扫描仪测量的 0.05 到 0.4 的光学密度范围。为了评估 EBT-2 型 GAFCHROMIC™胶片在深度剂量测量中的精度，研究了测量的光学密度随胶片之间和扫描仪床之间的均匀性变化的不确定性。
对于大多数光束，EBT-2 型 GAFCHROMIC™胶片测量的百分深度剂量与使用电离室测量的结果非常吻合。在某些情况下（i）千伏 X 射线在较大深度处由于束硬化，以及（ii）在布拉格峰附近的质子束由于淬灭效应，会出现一些差异。对于这些光束，使用经验多项式校正会产生与电离室数据更好的一致性。
EBT-2 型 GAFCHROMIC™胶片是一种出色的二次剂量计，可用于测量放射治疗中广泛使用的各种光束质量和模式的百分深度剂量。它提供了一种简单高效的方法，可使用高空间分辨率测量光束深度剂量数据。
