RADT-84. LOW-DOSE WHOLE BRAIN RADIOTHERAPY AS AN EFFECTIVE CONSOLIDATION STRATEGY IN SECONDARY CENTRAL NERVOUS SYSTEM LYMPHOMA

Abstract INTRODUCTION Optimal consolidation strategies for secondary central nervous system lymphoma (SCNSL) are not well defined. Autologous stem cell transplant (ASCT) has shown promise, but alternatives are needed for ASCT-ineligible patients. Whole brain radiotherapy (WBRT) is an alternative in primary central nervous system lymphoma, but it has not been studied in SCNSL. METHODS We evaluated SCNSL patients at MSKCC who received consolidative brain radiotherapy (RT) after achieving a complete (CR) or partial response (PR) to induction therapy. Patients receiving ASCT were excluded. Low-dose RT was defined as ≤25 Gy. CNS relapse was determined by imaging or cytology; overall survival (OS) was calculated from RT start using Kaplan-Meier. RESULTS Eight patients were identified (median age 65, range 34–73; median KPS 90). All had diffuse large B-cell histology; two developed SCNSL de novo and six at relapse. Seven received methotrexate (MTX)-containing induction. The median interval from last MTX dose to RT was 51 days (21–115). At RT, five patients were in CR and three in PR. No patients had leptomeningeal or extra-cranial disease at RT. Median RT dose was 24 Gy (23.4–45 Gy) over 13 fractions (10–25); five patients received low-dose RT. WBRT was used in seven cases and partial-brain in one. Five patients received subsequent non-myeloablative systemic therapy (cytarabine (4), rituximab (1), Polatuzumab-vedotin/bendamustine/rituximab (1)). With median follow-up of 49 months (range 15–198), median OS was not reached; estimated 5-year OS was 60% (95% CI 25–96%). The three patients in PR converted to CR after RT. There were two CNS relapses outside the RT field (lumbar nerve root and ocular), and two extra-cranial relapses. DISCUSSION In this small cohort, low-dose WBRT consolidation correlated with encouraging long-term survival. Absence of leptomeningeal or extra-cranial disease at RT are potential criteria for patient selection. These results support further investigation of low-dose WBRT consolidation for SCNSL patients who are unsuitable for ASCT.