Stereotactic external beam calculations for radiosurgical treatment of brain lesions

Radiosurgical techniques are becoming increasingly popular for the selective destruction of brain lesions. To ensure precision in the procedure, set-up and treatment of lesions in this manner, we have adopted standard stereotactic methods to allow one to calculate accurately the absorbed dose and also to preserve accuracy in locating the target site in three dimensions. At McGill University, radiosurgery is performed using the dynamic technique, which utilizes the concurrent rotation of both the 10-MV photon beam linear accelerator (from 30 to 330 degrees) and the patient couch (from 75 to -75 degrees) about a common point centered on the target within the lesion. A three-dimensional treatment planning system for the calculation of dose distributions implemented in conjunction with CT, MRI and DSA stereotactic image analysis systems is presented.