Proton Beam Therapy for Adolescent Primary Central Nervous System Lymphoma With Residual Tumor After Intensive Chemotherapy: A Case Report

Primary central nervous system lymphoma (PCNSL) is a very rare type of non-Hodgkin lymphoma. Although pediatric and adolescent PCNSL patients generally respond well to intensive chemotherapy, the salvage treatment for this condition remains uncertain for patients exhibiting a poor/suboptimal response to primary therapy. Proton beam therapy (PBT) is being increasingly employed especially for pediatric oncology cases. However, the safety and feasibility of PBT for PCNSL patients have not been addressed. We encountered an adolescent patient with PCNSL exhibiting 4 of 5 adverse prognostic factors at diagnosis and a residual tumor adjacent to the pituitary gland with gadolinium enhancement on brain magnetic resonance imaging after 7 courses of intensive chemotherapy. We selected local PBT at a dose of 30.6 Gy (relative biological effectiveness) as a salvage treatment for the residual tumor. After PBT, gadolinium enhancement of the residual lesion rapidly disappeared with no acute adverse effects. Moreover, during 30 months of follow-up, no neurological or endocrinological adverse effects have been observed despite the location of the tumor. The patient is now healthy and has shown no evidence of relapse. PBT deserves further investigation as a salvage treatment option for PCNSL patients exhibiting a suboptimal response to primary chemotherapy.