Dosimetric considerations on multiple arc stereotaxic radiotherapy.

The aim of this paper is to present the physical and dosimetrical features of the stereotaxic radiosurgical method already published by the authors. This method concentrates the dose into the stereotaxic target volume, placed at the isocenter of a 4 MV X-ray beam. Computer calculations showed that: 9-17 arcs provide almost spherical dose distributions; the optimal photon beam quality is about 4-6 MV. The angle between adjacent rotation planes is 20-40 degrees and the arcs are 100-160 degrees wide. In this way the dose to healthy tissue is minimized. The dose distribution was experimentally verified both by ionometric and photodensitometric methods. The procedure for dose calculation at isocenter of fields as small as required by the radiotherapist, has been investigated.