Purpose: Gamma Knife (GK) radiosurgery has recently been employed in patients with numerous brain metastases (METs), even those with 10 or more lesions. However, cumulative irradiation doses to the whole brain (WB), with such treatment, have not been determined.
Methods and materials: Since the GammaPlan ver. 5.10 (ver. 5.31 is presently available, Leksell GammaPlan) became available in November 1998, 92 GK procedures have been performed for 80 patients with 10 or more brain METs at our facility. The median lesion number was 17 (range: 10-43) and the median cumulative volume of all tumors was 8.02 cc (range: 0.46-81.41 cc). The median selected dose at the lesion periphery was 20 Gy (range: 12-25 Gy). Based on these treatment protocols, the cumulative irradiation dose was computed.
Results: The median cumulative irradiation dose to the WB was 4.71 (range: 2.16-8.51) Gy. The median brain volumes receiving >2 Gy, >5 Gy, >10 Gy, >15 Gy, and >20 Gy were 1105 (range 410-1501) cc, 309 (46-1247) cc, 64 (13-282) cc, 24 (2-77) cc, and 8 (0-40) cc, respectively.
Conclusion: The cumulative WB irradiation doses for patients with numerous radiosurgical targets were not considered to exceed the threshold level of normal brain necrosis.