Risk of radiation necrosis after stereotactic radiosurgery for melanoma brain metastasis by anatomical location.

PURPOSE: In this retrospective study, we have explored the anatomical factors that lead to the development of radiation necrosis (RN) in the setting of stereotactic radiosurgery (SRS) for melanoma brain metastases (MBM). METHODS: Between 2014 and 2018, 137 patients underwent SRS for 311 MBM. Lesions were assessed according to anatomical zones: zone 1-peripheral grey-white matter junction and cortical mantle, zone 2-deep white matter, including tumours located at base of sulci, zone 3-tumours adjacent to ependymal lining or in deep locations such as brainstem, basal ganglia and thalamus. Other anatomical factors including lobes, medial-peripheral, supra or infratentorial locations were also recorded. RESULTS: In all, 12.4% (n = 17) of patients and 6.1% (n = 20) of lesions developed RN, actuarial incidence of RN at 12 and 24 months was 10% and 14.2% respectively. Zone 2 lesions recorded the highest rate of development of RN (n = 7/19; 36%), zone 3 (N = 4/24; 16%) and zone 1 (n = 9/268; 3%). Five of 17 patients developed symptomatic RN and 7/17 patients underwent surgery for RN. CONCLUSION: This study raises awareness of the increased likelihood of deep lesions particularly in white matter structures to develop RN after SRS. Further studies including larger cohorts would be useful in identifying statistical differences in the rate of development of RN in different anatomical zones.