Rice R K, Hansen J L, Chin L M, Mijnheer B J, Bjärngard B E
Department of Radiation Therapy, Harvard Medical School, Boston, Massachusetts 02115.
Med Phys. 1988 Nov-Dec;15(6):884-90. doi: 10.1118/1.596171.
Lung dose correction factors, commonly defined as the ratios of ionization chamber readings in the heterogeneous and homogeneous phantoms, have been compared with those based on accurately determined doses. An analysis of stopping power values, Pwall values, and measurements in lunglike and waterlike materials showed that the wall material and thickness are not very critical in the determination of lung dose correction factors under conditions of electronic equilibrium. When lateral electronic equilibrium is not established due to the extended range of scattered electrons in the low density material, Prepl differs significantly from unity for ionization chambers with thick walls which do not match the lung material in density. An attempt has been made to characterize this effect as a function of photon energy, lung density, field size, and wall thickness.
肺剂量校正因子通常定义为非均匀模体和均匀模体中电离室读数的比值，已将其与基于精确测定剂量的校正因子进行了比较。对阻止本领值、Pwall值以及在类肺材料和类水材料中的测量结果进行分析表明，在电子平衡条件下，壁材料和厚度对于确定肺剂量校正因子并非非常关键。当由于低密度材料中散射电子的射程扩展而未建立横向电子平衡时，对于壁厚且密度与肺材料不匹配的电离室，Prepl显著不同于1。已尝试将这种效应表征为光子能量、肺密度、射野大小和壁厚的函数。
