Experience in implementing the Mark III Rad 8 system for radiotherapy dose computations.

Abstract

Rad 8 is a small, in-house computer system for calculating radiotherapy dose distributions, both for multiple field and rotational external beam techniques and for interstitial and intracavitary redium treatments. Implementing the system has its difficulties, particularly in obtaining the necessary beam profile information. Several approaches have been tried and finally a separate profile generator program was written. Other difficulties encountered with beam data storage were overcome by making minor changes to the system programs. The various calculation techniques have been evaluated, and in general found to be satisfactory, and suitable factors to be used in the inhomogeneity correction for 4 MV X rays have been calculated based on previously published measured data. An option to change beam weightings exists and this can be used to renormalize dose distributions to give percentage isodose curves relative to the prescribed tumour dose. If this procedure is followed dose homogeneity over the target volume can readily be assessed, and the exposure times may easily be calculated from the new weightings. Certain shortcomings in the rotating beam program and the radium program may easily lead to error if extreme care is not exercised.