STEREOTAXIC TREATMENT OF BRAIN-TUMORS WITH RADIOACTIVE IMPLANTS OR EXTERNAL PHOTON BEAMS - RADIOBIOPHYSICAL ASPECTS

We perform calculations, based on the linear-quadratic model, to assess the biologically effective doses (BED) of tumor and normal tissue in the stereotactic irradiation of brain tumors with either radioactive implants or radiosurgery techniques. Treatment protocols for radiosurgery and radioactive implants, as obtained from the literature, are reviewed and compared. A figure of merit is defined to be the ratio of tumor to normal tissue BED, expressed in units of Gy10/Gy3. These comparisons indicate a clear radiobiological advantage for brachytherapy, unless the radiosurgery is to be delivered in a large number of fractions. The differences in dose uniformity, and in the volume of normal tissue encompassed by the high dose regions, are factors that may also influence clinical results.