A TECHNIQUE FOR FRACTIONATED STEREOTAXIC RADIOTHERAPY IN THE TREATMENT OF INTRACRANIAL TUMORS

Purpose: The excellent treatment results obtained with traditional rad iosurgery have stimulated attempts to broaden the range of intracrania l disorders treated with radiosurgical techniques. For major users of radiosurgery this resulted in a gradual shift from treating vascular d iseases in a single session to treating small, well delineated primary tumors on a fractionated basis. In this paper we present the techniqu e currently used in Montreal for the fractionated stereotactic radioth erapy of selected intracranial lesions. Methods and Materials: The reg imen of six fractions given every other day has been in use for ''frac tionated stereotactic radiotherapy'' in our center for the past 5 year s. Our current irradiation technique, however, evolved from our initia l method of using the stereotactic frame for target localization and f irst treatment, and a ''halo-ring'' with tattoo skin marks for the sub sequent treatments. Recently, we developed a more precise irradiation technique, based on an in-house-built stereotactic frame which is left attached to the patient's skull for the duration of the fractionated regimen. Patients are treated with the stereotactic dynamic rotation t echnique on a 10 MV linear accelerator (linac). Results: In preparatio n for the first treatment, the stereotactic frame is attached to the p atient's skull and the coordinates of the target center are determined . The dose distribution is then calculated, the target coordinates are marked onto a Lucite target localization box, and the patient is plac ed into the treatment position on the linac with the help of laser pos itioning devices. The Lucite target localization box is then removed, the target information is tattooed on the patient's skin, and the pati ent is given the first treatment. The tattoo marks in conjunction with the target information on the Lucite target localization box are used for patient set-up on the linac for the subsequent 5 treatments. The location of the target center is marked with radio-opaque markers on t he target localization box and verified with a computerized tomography scanner prior to the second treatment. The same verification is done prior to other treatments when the target center indicated by the targ et localization box disagrees with that indicated by the tattoo marks. The new position of the target center is then determined and used for treatment positioning. Conclusion: The in-house-built frame is inexpe nsive and easily left attached to the patient's skull for the 12 day d uration of the fractionated regimen. Positioning with the Lucite targe t localization box verified with tattoo marks ensures a high level of precision for individual fractionated treatments.