Abstract: Objective To analyze recurrence and progression patterns of primary central nervous system lymphoma (PCNSL) in patients without whole brain radiotherapy (WBRT) and assess the value of WBRT in PCNSL treatment. Methods This retrospective single-center study included 27 patients with PCNSL, who experienced recurrence/progression after achieving complete remission (CR), partial remission, or stable disease following initial treatments with chemotherapy but without WBRT. The patients were followed up regularly after the treatment for treatment efficacy assessment. By comparing the anatomical location of the lesions on magnetic resonance images (MRI) at the initial diagnosis and at recurrence/progression, we analyzed the patterns of relapse/progression in patients with different treatment responses and different initial status of the lesions. Results MRI data showed that in 16 (59.26%) of the 27 patients, recurrence/progression occurred in out-field area (outside the simulated clinical target volume [CTV]) but within the simulated WBRT target area in 16 (59.26%) patients, and within the CTV (in-field) in 11 (40.74%) patients. None of the patients had extracranial recurrence of the tumor. Of the 11 patients who achieved CR after the initial treatments, 9 (81.82% ) had PCNSL recurrences in the out-field area but within WBRT target area; of the 13 patients with a single lesion at the initial treatment, 11 (84.62% ) experienced PCNSL recurrence in the out-field area but within WBRT target area. Conclusions Systemic therapy combined with WBRT still remains the standard treatment for PCNSL patients, especially those who achieve CR after treatment or have a single initial lesion. Future prospective studies with larger sample sizes are needed to further explore the role of low-dose WBRT in PCNSL treatment.

Key words: primary central nervous system lymphoma, radiation therapy, whole brain radiotherapy, recurrence/progression pattern