Analysis of dose distribution in gamma knife radiosurgery for multiple targets

Purpose: The aim of this study is to evaluate the actual effect of irradiation for other targets in dose planning for the treatment of multiple metastases 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 dose plans with every attempt to include as many targets as possible and calculate dose distributions separately for each dose matrix. We also calculated 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 dose distribution and the composite one ranged from 0.0 to 4.5 Gy with a mean of 1.5 Gy and was more than 2 Gy in 12 (24%) targets. The difference tended to be larger when targets were small in volume and/or the number of targets 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 targets treated in one session