Background: The use of Gamma Knife stereotactic radiosurgery (GKSRS) for the treatment of extensive intracranial metastases has been expanding due to its superior dosimetry and efficacy. However, there remains a dearth of data regarding the dose parameters in actual clinical scenarios. We endeavored to calculate the radiation dose to the brain when treating >15 brain metastases with GKSRS.
Methods: This retrospective analysis reviewed dosage characteristics for patients requiring single session GKSRS for the treatment of ³15 brain metastases. Forty-two patients met the inclusion criteria between 2008 and 2017. The median number of tumors at the initial GKSRS procedure was 20 (15-39) which accounted for 865 tumors in this study. The median aggregate tumor volume was 3.1cm3(0.13-13.26) and the median marginal dose was 16Gy (14-19Gy).
Results: The median of the mean brain dose was 2.58Gy (range 0.95-3.67Gy) and 79% of patients had a dose <3Gy. The 12Gy dose volume was a median of 12.45cm3, which was equivalent to 0.9% of the brain volume. The median percentage of brain receiving 5Gy and 3Gy was 6.7% and 20.4%, respectively. There was no correlation between the number of metastases and the mean dose to the brain (p=0.8). A higher tumor volume was significantly associated with an increased mean brain dose (p<0.001). The median of the mean dose to the bilateral hippocampi was 2.3Gy. Sixteen patients had supplementary GKSRS, resulting in an additional mean dose of 1.4Gy (0.2-3.8Gy) to the brain.
Conclusion: GKSRS is a viable means of managing extensive brain metastases. This procedure provides a relatively low dose of radiation to the brain, especially when compared to traditional whole brain radiation protocols.