A simple model for examining issues in radiotherapy optimization

Convolution/superposition software has been used to produce a library of ph oton pencil beam dose matrices. This library of pencil beams is designed to serve as a tool for both education and investigation in the held of radiot herapy optimization. The elegance of this pencil beam model stems from its cylindrical symmetry. Because of the symmetry,the dose distribution for a p encil beam from any arbitrary angle can be determined through a simple rota tion of a pre-computed dose matrix. Rapid dose calculations can thus be per formed while maintaining the accuracy df a convolution/superposition based dose computation. The pencil beam data sets have been made publicly availab le. It is hoped that the data sets will facilitate a comparison of a variet y of optimization and delivery approaches. This paper will present a number of studies designed to demonstrate the usefulness of the pencil beam data sets. These studies include an examination of the extent to which a treatme nt plan can be improved through either an increase in the number of beam an gles and/or a decrease in the collimator size. A few insights into,the sign ificance of heterogeneity corrections for treatment planning for intensity modulated radiotherapy will also be presented. (C) 1999 American Associatio n of Physicists in Medicine. [S0094-2405(99)02007-6].