Computer and Approximation Methods of Calculating Depth Dose in Irregularly Shaped Fields

A computer program was developed to calculate depth dose in irregularly shaped fields. The program is general for any shaped field and includes corrections for variations of exposure rate within the field, body contour, and non-nominal source-skin distances. Depth doses were calculated in several actual cases involving irregular fields such as mantle, split, L-shaped, and inverted Y fields. Data were examined to determine the degree of dose inhomogeneity in these fields. An approximation method used in the irregular field dosimetry was evaluated with regard to its accuracy and limitations. Comparison of depth dose determinations using both methods showed a discrepancy of only 2 to 3%.