10MV X線照射における側方電子平衡不成立領域でのファントム散乱補正係数

概要

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Using the Fano theorem, we determined the minimum square field that can establish lateral electron equilibrium in water for 10 MV x-rays. The minimum square field is 3.5×3.5 cm^2. This field size is the same as that proposed by Iwasaki. In addition, we obtained a set of phantom scatter correction factors (S_p) at small fields providing lateral electron nonequilibrium and then supplied the S_p data to the 3-D radiation treatment planning system called FOCUS. Using the planning system, we produced tissue-phantom ratio (TPR) data from measured percentage depth dose (PDD) data. It was found that the zero-area TPR obtained by extrapolation has two different values, one obtained using TPR data at fields greater than 3.5×3.5 cm^2 and the other obtained using TPR data at fields smaller than 3.5×3.5 cm^2.
社団法人日本放射線技術学会の論文
1998-03-20