A prospective phase II trial of response adapted whole brain radiotherapy after high dose methotrexate based chemotherapy in patients with newly diagnosed primary central nervous system lymphoma-analysis of acute toxicity profile and early clinical outcome

The treatment of primary CNS lymphoma (PCNSL) comprises high dose methotrexate (HDMTX) based chemotherapy followed by whole brain radiotherapy (WBRT), the major drawback of which is long term neurotoxicity. We intended to assess the feasibility of response adapted WBRT in PCNSL in the Indian setting. We screened 32 patients and enrolled 22 eligible patients with PCNSL from 2015 to 2017 in a prospective phase II trial. The patients underwent five 2-weekly cycles of induction chemotherapy with rituximab, methotrexate, vincristine, procarbazine. Patients with complete response(CR) to induction chemotherapy were given reduced dose WBRT 23.4 Gy/13 fractions/2.5 weeks while those with partial response (PR), stable or progressive disease (SD or PD) were given standard dose WBRT 45 Gy/25 fractions/5 weeks. Thereafter two cycles of consolidation chemotherapy with cytarabine were given. The primary endpoints of the study were assessment of response rate (RR) and progression free survival (PFS). The secondary endpoints of the study were assessment of overall survival (OS), toxicity profile of treatment and serial changes in quality of life and neuropsychological parameters. Out of 19 patients who completed HDMTX based chemotherapy, 10 (52.63%) patients achieved CR, 8 (42.11%) patients had PR and 1 patient had PD. After a median follow-up period of 11.25 months, the estimated median OS was 19 months. The actuarial rates of PFS and OS were respectively 94.1 and 68.2% at 1 year and 50.2 and 48.5% at 2 years. Three patients in reduced dose WBRT arm had recurrence and two of them died of progressive disease, whereas there was no recurrence or disease related death in standard dose WBRT arm. On univariate analysis of PFS, age ae<currency> 50 years and use of standard dose WBRT (45 Gy) led to significantly improved outcome (p value 0.03 and 0.02 respectively). In patients with PCNSL, reduced dose WBRT after CR to HDMTX based chemotherapy may lead to suboptimal clinical outcome due to higher risk of recurrence, progression and early death. Trial Registration No CTRI/2015/10/006268.