Percentage depth doses for high energy X-rays

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Abstract
Percentage depth doses for 34 MV betatron X-rays were measured ionometrically for a number of square fields of side 5-20 cm. Significant differences in the depth doses for different field sizes were found in the build-up region and in the depth of maximum dose. A systematic change with depth was also indicated in the exponential region of these curves. These differences are discussed in terms of the changes in the contributions of primary radiation and of scattered radiation from both the collimator and the phantom.