THE HEAD-SCATTER FACTOR FOR SMALL-FIELD SIZES

被引:63
作者
ZHU, TC
BJARNGARD, BE
机构
[1] Department of Radiation Oncology, Roger Williams Cancer Center, Brown University, Providence, Rhode Island
关键词
HEAD-SCATTER FACTOR; COLLIMATOR SCATTER; OUTPUT FACTOR; SOURCE PROFILE; SMALL FIELD SIZES;
D O I
10.1118/1.597256
中图分类号
R8 [特种医学]; R445 [影像诊断学];
学科分类号
1002 ; 100207 ; 1009 ;
摘要
The head-scatter factors H were examined for four different linear accelerators and were found to be similar at field sizes larger than 3 X 3 cm(2). Sharply reduced values for small collimator openings were observed for all the accelerators. It is concluded that the head-scatter tot collimator-scatter) factor has two major components. Scatter of photons in various structures in the beam path, especially the flattening filter, causes a slow (about 10%) increase with increased collimator opening. Insertion of a built-in wedge may double this number. When the collimators are closed, they ultimately block photons from the periphery of the source. This may cause a considerable reduction of the primary photon fluence and typically affects fields smaller than 3 X 3 cm(2). The effect can be used to estimate the source size, with results that correlate with the design of the bending magnet.
引用
收藏
页码:65 / 68
页数:4
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