Three-dimensional isodose distributions in stereotactic radiosurgery.

A personal computer based three-dimensional treatment planning system, which may be used for planning any linear accelerator (Linac) based radiosurgical technique, is presented. The system is used to calculate dose distributions for most of the Linac-based techniques currently in use as well as the theoretically optimum 4 pi geometry. The maximum and minimum dose falloffs are used to compare the various Linac-based radiosurgical techniques. The dynamic rotation technique developed at McGill University is shown to produce distributions with dose falloffs similar to the multiple converging arc techniques used elsewhere and those obtained for the Gamma Unit. Also considered are the effects of beam energy, in the range of 4-25 MV, and beam profiles on the dose distribution.