DOSE ACCURACY CHECK OF THE 3D ELECTRON-BEAM ALGORITHM IN A TREATMENT PLANNING SYSTEM

The accuracy of the recently implemented three-dimensional electron be am dose calculating algorithm in CADPLAN version 2.62 manufactured by Varian Dosetek was investigated. The algorithm uses a generalized Gaus sian pencil beam model and the dose distributions are calculated as th e sum of three weighted Gaussians. To use the calculating program in a n optimum way, one needs to know the dose calculation accuracy of the algorithm as well as its limitations. This investigation includes comp arisons of measured relative dose distributions with calculated dose d istributions and also comparisons of measured and calculated monitor u nits. The geometries tested were quadratic fields, irregularly shaped fields, oblique fields, irregularly shaped phantom surfaces and intern al heterogeneities and were most often irradiated with 8 and 20 MeV el ectrons. The results indicate that the algorithm is well suited for cl inical three-dimensional dose planning. Some deviations occurred but t hey were most often within the limits of international criteria of acc eptability.