Abstract
We evaluated the method of multi-fractionated stereotactic radiotherapy using the linear accelerator with soft and painless fixation for selected patients with intracranial tumors. Stereotactic radiotherapy became available as a result of being able to evaluate the characteristics required for dose calculation, flatness of the dose distribution and dose measurement methods in small radiation fields. Dose distributions with and without various size cones for the narrow beam were calculated by film dosimetry. The absorbed doses at several reference points were calculated with an Si-semiconductor detector, shallow ionization chamber or a JARP (Japanese Association of Radiological Physicists) dosimeter. The results of the calculations suggested that the use of cones was useful to achieve a flat dose distribution and that the Si-semiconductor detector was better for narrow-beam dose calculations than other dosimeters. We simulated stereotactic radiotherapy for intracranial lesions fifteen times using a human head phantom and delivered 200cGy per fraction to a target point in the phantom. The mean absorbed doses for the calculated doses at the target point was 206cGy. We concluded that the Si-semiconductor detector with the smallest sensitive volume is the most suitable field dosimeter, and our methods of fractionated stereotactic radiotherapy were corroborated by an assessment of factors that might cause dose uncertainty.
