Tello V M, Tailor R C, Hanson W F
Department of Radiation Physics, University of Texas M.D., Anderson Cancer Center, Houston 77030, USA.
Med Phys. 1995 Jul;22(7):1177-89. doi: 10.1118/1.597613.
The water equivalency of five "water-equivalent" solid phantom materials was evaluated in terms of output calibration and energy characterization over a range of energies for both photon (Co-60 to 24 MV) and electron (6-20 MeV) beams. Evaluations compared absorbed doses calculated from ionization measurements using the same dosimeter in the solid phantom materials and in natural water (H2O). Ionization measurements were taken at various calibration depths. The Radiological Physics Center's standard dosimetry system, a Farmer-type ion chamber in a water phantom, was used. Complying with the TG-21 calibration protocol, absorbed doses were calculated using eight measurement and calculational techniques for photons and five for electrons. Results of repeat measurements taken over a period of 2 1/2 years were reproducible to within a +/- 0.3% spread. Results showed that various combinations of measurement techniques and solid phantom materials caused a spread of 3%-4% in the calculation of dose relative to the dose determined from measurements in water for all beam energies on both modalities. An energy dependence of the dose ratios was observed for both photons and electrons.
在一系列能量范围内，针对光子（钴 - 60至24兆伏）和电子（6至20兆电子伏）束，从输出校准和能量特性方面评估了五种“水等效”固体模体材料的水等效性。评估比较了在固体模体材料和天然水（H₂O）中使用相同剂量计通过电离测量计算得到的吸收剂量。电离测量在不同校准深度进行。使用了放射物理中心的标准剂量测定系统，即水模体中的 Farmer 型电离室。按照TG - 21校准协议，光子使用八种测量和计算技术、电子使用五种测量和计算技术来计算吸收剂量。在2年半时间内进行的重复测量结果的重现性在±0.3%的范围内。结果表明，对于两种模式下的所有束能量，测量技术和固体模体材料的各种组合在剂量计算中相对于水中测量确定的剂量产生了3% - 4%的差异。对于光子和电子，均观察到剂量比的能量依赖性。
