33 Is hypofractionation safer than single-fraction radio surgery? The effect of fractionation on radionecrosis

Introduction: Radiation-induced brain necrosis (RN) is a relatively uncommon (5-20%) but potentially severe adverse effect of stereotactic radiosurgery (SRS) for brain metastasis(BM). We attempted to establish the effect of hypo-fractionation on RN rates by reviewing patients having simultaneous multi-fraction and single fraction treatment of BM at our centre. Methods: Patients receiving simultaneous 1 (20-24Gy) or 3 fraction (21-24Gy) SRS treatments were identified in our institution’s database. Serial post-SRS MRIs were reviewed to determine the lesion quotient (LQ), or maximum cross sectional area on T1 plus gadolinium divided by T2 FLAIR sequences. LQ less than 0.3 was considered RN. Result: Twenty-two patients were followed for a median 320 days. Sixteen patients developed radionecrosis in 21 of 62 lesions (33%), four of which were symptomatic (20%). Eleven of these lesions received 3 fractions and ten received one fraction. RN risk increased with increasing tumor volume (log odds ratio=1.12, p=0.04). There was no difference in incidence of RN in patients who received whole brain radiotherapy (WBRT) (p=0.11), hypo-fractionation (p=0.98) or had a higher maximum dose (p=0.71). Radiographic RN, however, did not clear in any patients who developed it. Eight patients developed a local recurrence (12%), six of which occurred in the single fraction group. Conclusion: Radionecrosis was significantly related to tumor volume but not fractionation, WBRT, or maximum dose. Overall, our results indicate patients receiving SRS for multiple brain metastasis have a higher rate of radionecrosis than the literature and poorer survival despite having equivalent local control.