2642 - Repeat Stereotactic Radiosurgery for Recurrent Brain Metastases: A Retrospective Comparison of Local Progression and Distant Brain Metastases after Prior Radiosurgery

Purpose/Objective(s): This study evaluates the efficacy and safety of repeat stereotactic radiosurgery (SRS) for recurrent brain metastases (BM), focusing on failure patterns of local progression (LP) and distant BM (DBM) after prior SRS.

Materials/Methods: Between 2011 and 2022, patients who received first-time SRS for newly diagnosed BM and underwent repeat SRS for recurrence up to June 2024 were included. Treatment courses were classified into first-time SRS and repeat SRS, with repeat courses subdivided into those treating local progression (LP) at prior SRS sites with or without DBM and those treating distant brain metastases (DBM) only. The primary endpoint was the 1-year local control rate (LCR), defined as the proportion of treatments without LP events after repeat SRS. Secondary endpoints included survival after repeat SRS (analyzed using the Kaplan-Meier method and log-rank test) and the incidence of radiation necrosis (RN). RN was graded based on the International Stereotactic Radiosurgery Society guidelines. Incidence was assessed across all groups using cumulative incidence analysis with death as a competing event and compared via Gray's test.

Results: Of the 723 treatment courses (427 patients, 4,524 BMs), 404 courses (141 patients, 2,924 BMs) met the study criteria. Of these, 141 patients received first-time SRS (141 courses, 775 BMs), followed by repeat SRS in 263 courses for the same patients with 2,149 BMs. Of the repeat courses, 45 courses (38 patients, 224 BMs) were classified as the LP group and 218 courses (126 patients, 1,925 BMs) as the DBM-only group. Median age was 65 years, with 46.1% being female. The most common primary tumor histology was lung cancer (75.9%), followed by breast (9.2%) and gastrointestinal cancer (7.8%). The median time from prior SRS to repeat SRS was 6.9 months (LP: 12.6 vs DBM: 6.3 months, P < 0.001), and the median follow-up time was 31.1 months from first-time SRS, 13.5 months from repeat SRS (LP: 12.4 vs DBM: 13.7 months, P = 0.791). The 1-year LCR was significantly lower in the LP group than in the DBM group (72.4% vs 88.3%, P = 0.0022). Median survival times were similar in both groups (LP: 17.9 vs DBM: 16.3 months, P = 0.345). The cumulative incidence of RN at 1 year was 5.7% for first-time SRS, 20.6% for repeat SRS for LP, and 5.7% for repeat SRS for DBM, with the LP group showing significantly higher incidence than the DBM group (P < 0.001) and higher symptomatic RN (grade =2) (13.3% vs 2.8%). No significant difference was found between first-time and repeat DBM groups (P = 0.070).

Conclusion: Patients with LP have a lower salvage rate and a higher risk of symptomatic RN despite having similar survival outcomes to those with only DBM, highlighting the need for prospective trials to determine the optimal radiation dose.