H. Murata, T. Ozawa, S. Sakamoto, H. Ushijima, T. Kodama, S. Hashimoto, T. Kojima, Y. Ozeki, N. Hayase, and S. Kudo; Saitama Cancer Center, Saitama, Japan
Purpose/Objective(s):Dose-dependent local control is known for stereotactic radiotherapy (SRT) of brain metastases (BM). We summarize here our experience with patients of BM treated by the high-dose SRT of 38 Gy or 35 Gy in 3 fractions. Materials/
Methods: This study is a retrospective review of all cases of BM treated by liniac-based SRT with dynamic conformal arcs technique at our institution from July 2014 to April 2023. The margin from gross tumor volume (GTV) to planning target volume (PTV) was 1-2 mm. The total dose of 38 Gy or 35 Gy was administered in 3 fractions, and the prescribed dose covered 95% of the PTV. We analyzed the impact of patient and treatment characteristics on overall survival (OS), local control (LC) and radionecrosis (RN) after SRT by Kaplan-Meier method and cox regression models. Statistical significance was set at p < 0.05. Results: There were 236 patients. The total number of lesions was 331, and the median follow-up period was 9.5 months (range: 0.1-106.5). Patients had a median age of 69 years (range: 35-92), 149 (63%) were male. The most common presenting illness was non-small-cell lung (NSCLC) cancer (120 patients, 51%), followed by breast cancer (33 patients, 14%), SCLC (25 patients, 11%), colorectal cancer (12 patients, 5%), esophageal cancer (8 patients, 3%), renal cell carcinoma (8 patients, 3%), gastric cancer (6 patients, 3%) and others (24 patients, 10%). The median GTV was 2.9 cc (IQR: 1.5-5.3). The dose of 38 Gy in 3 fractions was prescribed for 251 lesions and 35 Gy in 3 fractions for 80 lesions. The median OS was 10.7 months, and the 6-months, 1-year, and 2-year OS rates were 65%, 47%, and 26%, respectively. In univariate analysis, the prognosis was significantly better in the group with good performance status, control of extracranial lesions, and chemotherapy after SRT, respectively. The LC rates at 6 months, 1 and 2 years were 97%, 93% and 91%, respectively, for all lesions. The total of 13 lesions (4%) had local recurrence, of which 7 lesions underwent surgery. There was no significant difference in LC rate between the 38 Gy and 35 Gy groups (p = 0.89). Symptomatic RN was observed in a total of 26 lesions (8%), of which 14 lesions underwent surgery. The cumulative incidence of symptomatic RN at 1 year, 2 years and 5 years was 4.7%, 17.2% and 42.5%, respectively. The cumulative incidence of RN requiring surgery at 1 year, 2 years and 5 years was 1.1%, 6.1%, and 32.8%, respectively. In univariate analysis, GTV =3 cc (vs. <3 cc) was associated with higher rates of RN, not with LC or OS. In 14 lesions with surgery for RN, the median surrounding brain volumes circumscribed with 18 Gy and 24 Gy were 28.8 cc (range: 13.9-57.4) and 19.2 cc (range: 8.3-36.3), respectively. Conclusion: While high-dose, three-fraction SRT for BM can be expected to have a high LC rate, it is necessary to be careful about RN in long-term survival cases with high exposure doses to the normal brain.
