Analytic representation of electron central‐axis depth dose data

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Abstract
A number of analytic representations of electron [radiotherapy] central-axis depth dose data current in the literature was examined and tested against sets of standard depth dose data. One of them, a 2-parameter model of Shabason and Hendee, is recommended in situations in which good accuracy (.apprx. 2%) is desired, with the values of the parameters determined by an approximation formula developed elsewhere. For higher accuracy, a polynomial model was developed which gives typically a standard deviation of the fitting polynomial from the data points of 1%, and a maximum deviation of 2%. Fitting polynomials obtained with this method possess the property of having zero slope at the position of actual maximum dose, and generally a 5th-order polynomial (requiring 4 nonzero coefficients) provided the most acceptable fit. The 4 parameters involved are determined through inversion of a 4 .times. 4 matrix, and these 4 coefficients were tabulated for the standard data sets. The polynomial model is designed for interpolation in the range between the 100% dose depth and the 10% dose depth, and another fitting curve of the same type can be adjoined to cover depths < 100% dose depth.
Funding Information
  • National Institutes of Health Postdoctoral Fellowship (5 F32 CA0610-02)