Analysis of dose distribution in Gamma Knife radiosurgery for multiple targets

Purpose: The aim of this study is to evaluate the actual effect of irradiat ion for other targets in dose planning for the treatment of multiple metast ases with Gamma Knife. Methods and Materials: We analyzed dose distributions for 51 targets in 10 patients with metastatic brain tumors who underwent radiosurgery with Gamma Knife for the treatment of more than one target in one session. We made do se plans,vith every attempt to include as many targets as possible and calc ulate dose distributions separately for each dose matrix, We also calculate d the composite dose distribution by including the effect of all shots used . We compared these noncomposite and composite dose distributions. Results: The differences in the mean target dose between the noncomposite d ose distribution and the composite one ranged from 0.0 to 4.5 Gy with a mea n of 1.5 Gy and was more than 2 Gy in 12 (24%) targets, The difference tend ed to be larger when targets were small in volume and/or the number of targ ets was large. Conclusions: The effect of irradiation from the shots for other targets was not negligible in some cases, This difference of dose distribution should be considered in the analysis of clinical outcomes of cases with multiple t argets treated in one session. (C) 2000 Elsevier Science Inc.