Dawson D J, Akinradewo A C
Med Phys. 1985 Jul-Aug;12(4):389-92. doi: 10.1118/1.595750.
Ionization chambers with wall materials of various electron densities have been employed to investigate the penumbral region of a cobalt-60 beam of side length 10 cm. Measurements were made in air with chambers of various inside diameters. The homogeneous walls of the ionization chambers were 0.5 g/cm2 in thickness. Extrapolation techniques to zero inside diameter and to infinite density were used, respectively, to eliminate the effect of the inside diameter of the chamber and to determine the penumbral photon-fluence distribution. The method also quantitates both the penumbral primary-dose profiles in water-equivalent media and the degradation of these profiles in media of low electron density.
已使用具有不同电子密度壁材料的电离室来研究边长为10厘米的钴 - 60射束的半影区。使用各种内径的电离室在空气中进行测量。电离室的均匀壁厚度为0.5 g/cm²。分别采用外推到零内径和无限密度的技术，以消除电离室内径的影响并确定半影光子注量分布。该方法还对水等效介质中的半影原剂量分布以及这些分布在低电子密度介质中的退化进行了定量。
