Abstract
Obtaining accurate attenuation of in-phantom primary water collision kerma is important for accurate evaluation of the in-phantom primary and scatter absorbed dose. Using a 10 MV x-ray beam generated by a linear accelerator with a lead flattening filter, we have developed a 10 MV x-ray attenuation coefficient expression for water as a function of depth (z) and off-axis distance (r), described herein. This paper also describes a 10 MV x-ray mean attenuation coefficient expression for water as a function of off-axis distance (r). From these, the following results have been obtained:(i) On any given fanline, the attenuation coefficient decreases exponentially with increasing z.(ii) At any given depth, the attenuation coefficient increases linearly with increasing r.(iii) The mean attenuation coefficient increases linearly with increasing r.(iv) For any given fanline, the mean attenuation coefficient derived from a set of transmission data for z=z0 to z0 is nearly equal to the attenuation coefficient for z=z0.
