Abstract：
: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 cm2. Sharply reduced values for small collimator openings were observed for all the accelerators. It is concluded that the head-scatter (or 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 cm2. The effect can be used to estimate the source size, with results that correlate with the design of the bending magnet.
journal_name
Med Physjournal_title
Medical physicsauthors
Zhu TC,Bjärngard BEdoi
10.1118/1.597256subject
Has Abstractpub_date
1994-01-01 00:00:00pages
65-8issue
1eissn
0094-2405issn
2473-4209journal_volume
21pub_type
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