Tissue phantom ratios for a Clinac 4/100

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Abstract
Tissue phantom ratios (TPR), based on a normalization depth of 5 cm, were measured in water for field sizes from 5 .times. 5 cm2 to .apprx. 40 .times. 40 cm2 and for depths from 1-40 cm for a Varian Clinac 4/100. These TPRs were compared with those calculated from percent depth doses measured at the same time, and the 2 sets of data generally agree to better than 1%, with an average ratio of measured to calculated TPR of 0.999 .+-. 0.013. Beam profiles have been measured for open and wedged fields, with particular concern for the often observed horns, or the increase in dose at the corners of the field. The maximum dose at a depth of 1 cm, along the diagonal of the field for this machine, is .apprx. 5% higher than at the same depth on the central axis, whereas along the principal plane the maximum dose is only .apprx. 3% higher.

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