Role of 23.4 Gy upfront whole-brain radiation therapy following high-dose methotrexate for primary central nervous system lymphoma: a comparative analysis of whole-brain radiation therapy versus no radiation therapy.

INTRODUCTION: We aimed to investigate the role of upfront whole-brain radiation therapy (RT), with a reduced dose of 23.4 Gy, following high-dose methotrexate (HD-MTX) in patients with primary central nervous system lymphoma (PCNSL).

METHODS: We retrospectively reviewed 185 patients with PCNSL treated with HD-MTX between January 2013 and January 2020; 145 patients underwent no RT and 40 patients underwent upfront RT. Using propensity score matching (PSM) to adjust for clinical factors, 40 patients were selected from each treatment group. Event-free survival (EFS) and overall survival (OS) were compared between treatment groups.

RESULTS: At baseline, patients in the upfront RT group were younger, had higher LDH levels, received less frequent rituximab and stem cell transplantation than those in the no-RT group. Patients in the upfront RT group also showed a lower response rate after initial HD-MTX than those in the no-RT group (73% vs. 88%, p = 0.038). The median follow-up was 25.1 (interquartile range 13.7-43.0) months. Comparable 2-year EFS and OS rates were observed between the upfront RT and no-RT groups (56.6% vs. 53.8%, p = 0.170; and 81.7% vs. 75.3%, p = 0.097, respectively). Upfront RT was related to improved EFS and OS in patients with stable disease or progressive disease after HD-MTX, but not in patients with complete or partial response after HD-MTX. Upfront RT was also an independent predictor of EFS and OS in the PSM cohort. The cumulative incidences of treatment-related neurotoxicity at 3 years were 20.2% and 21.2% in the upfront RT and no-RT groups, respectively (p = 0.630).

CONCLUSIONS: Upfront RT with a reduced dose of 23.4 Gy, showed favorable outcomes in patients with stable disease or progressive disease after initial HD-MTX. In addition, upfront RT appears to be an effective treatment for PCNSL when rituximab or stem cell transplantation is not feasible.