On beam quality and stopping power ratios for high-energyx-rays

Abstract

The aim of this work is to quantitatively compare two commonly used beamquality indices, TPR(20/10) and %dd(10)x, with respect totheir ability to predict stopping power ratios (water to air), sw,air, for high-energy x-rays. In particular, effects due to a varied amountof filtration of the photon beam will be studied. A new method forcharacterizing beam quality is also presented, where the information we striveto obtain is the moments of the spectral distribution. We will show how themoments enter into a general description of the transmission curve and that itis possible to correlate the moments to sw,air with a unique andsimple relationship. Comparisons with TPR(20/10) and%dd(10)x show that the moments are well suited for beam qualityspecification in terms of choosing the correct sw,air.