Hunt M A, Malik S, Thomason C, Masterson M E
Med Phys. 1984 Nov-Dec;11(6):806-13. doi: 10.1118/1.595568.
A comparison of the AAPM "Protocol for the determination of absorbed dose from high-energy photon and electron beams" (TG21) with currently used protocols for electron and photon dosimetry is presented. These protocols are the International Commission on Radiation Units and Measurements Report 21, "Radiation Dosimetry: Electrons with Initial Energies Between 1 and 50 MeV" (ICRU21), and the AAPM "Protocol for the Dosimetry of X- and Gamma Ray Beams with Maximum Energies Between 0.6 and 50 MeV" (SCRAD). Assuming a given radiation exposure and chamber parameters, doses to water at dmax for electron beams and at 5 g/cm2 for photon beams are calculated using the three protocols and then compared. The doses for photon beams calculated using the TG21 and SCRAD protocols are found to differ by 3% or less at energies below 10 MeV. The largest differences occur in photon doses at high energies where the dose calculated with the TG21 protocol is as much as 5.5% greater than that calculated with the SCRAD protocol for a typical thimble ionization chamber. For low electron beam energies, the doses calculated with the ICRU21 protocol are as much as 5% less than TG21 doses when using thimble chambers constructed of tissue-equivalent materials in a water phantom. If dosimetry measurements are performed in polystyrene, the dose calculated using TG21 may be greater than the ICRU21 dose, depending on chamber size and composition. An explanation for some of the differences between the protocols is presented emphasizing the dependence on chamber geometry, chamber composition, and phantom composition.
本文对美国医学物理师协会（AAPM）的“高能光子和电子束吸收剂量测定协议”（TG21）与当前使用的电子和光子剂量测定协议进行了比较。这些协议分别是国际辐射单位与测量委员会报告21《辐射剂量学：初始能量在1至50 MeV之间的电子》（ICRU21）以及AAPM的“最大能量在0.6至50 MeV之间的X射线和γ射线束剂量测定协议”（SCRAD）。假设给定辐射暴露和电离室参数，使用这三种协议计算电子束在dmax处以及光子束在5 g/cm²处对水的剂量，然后进行比较。发现在能量低于10 MeV时，使用TG21和SCRAD协议计算的光子束剂量差异在3%或更小。最大差异出现在高能量光子剂量中，对于典型的指形电离室，使用TG21协议计算的剂量比使用SCRAD协议计算的剂量高出多达5.5%。对于低能量电子束，当在水模体中使用由组织等效材料制成的指形电离室时，使用ICRU21协议计算的剂量比TG21剂量低多达5%。如果在聚苯乙烯中进行剂量测定测量，根据电离室尺寸和组成，使用TG21计算的剂量可能大于ICRU21剂量。本文给出了这些协议之间一些差异的解释，强调了对电离室几何形状、电离室组成和模体组成的依赖性。
