3414 - Radiotherapy for Marginal Zone Lymphoma of Mucosal Associated Lymphoid Tissue (MALT) Involving the Dura

Z. R. Moore¹, G. Cederquist², B. Fregonese², J. Yahalom², and B. S. Imber¹; ¹Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, ²Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): Marginal zone lymphoma (MZL) of the dura is low grade B-cell lymphoma that occurs rarely and has no established standard of care for treatment. Though they are generally indolent, patients often present with acute neurologic symptoms due to mass effect in the central nervous system. Dural relapse of MZL originating from nodal or extranodal sites may also occur. Treatment with surgery, radiotherapy (RT), intravenous, or intrathecal chemotherapy have been reported. Based on a growing body of evidence that very low dose radiotherapy is effective for extracranial low grade lymphomas, we hypothesized that low dose radiotherapy would result in durable local control for dural based MZL. We completed a retrospective review of patients treated with RT for MZL involving the dura to investigate local control and out-of-field relapse in relation to radiation dose and target volumes. Materials/

Methods: Patients treated with RT for MZL involving the dura at our institution were identified by medical chart review. Relapse after the initial course of radiation for dural-based disease on imaging was documented as either within or outside of the high dose field of radiation. Central nervous system progression was determined based on MR imaging or clinical symptoms of progression at follow up if imaging was not obtained. Kaplan-Meier analysis was used to determine median freedom from progression, with censoring at most recent follow up or imaging.
Results: Seventeen patients were identified who received RT between 2003 and 2022 as a component of their treatment. Fifteen patients (88%) had cranial dural disease, and two patients had dural involvement of the spine. Up front surgical resection was completed in 12 patients with a gross total resection in two patients. Four patients had relapsed disease at the time of RT, and three patients received chemotherapy prior to RT. One patient was treated with RT bridging prior to CAR-T therapy. Radiotherapy doses ranged from 4 Gy in 2 fractions to 42 Gy in 28 fractions, with 53% of patients receiving focal RT to involved sites and 47% of patients receiving whole brain radiotherapy with or without a boost. Six patients (35%) were treated with low dose RT between 4 Gy and 24 Gy. With a median follow up of 57 months, there were no recurrences within the radiation field, but seven patients (41%) had systemic relapse with a median freedom from progression of 8 years. Five patients received chemotherapy or rituximab after relapse. Two patients had orbital relapse outside of the RT field, both also had systemic relapse. There were 4 cases of severe late effects possibly related to RT (glioblastoma, cerebral small vessel disease, ulcerative colitis complications), all in patients who received doses of 30 Gy or higher.
Conclusion: With excellent local control and the goal of minimizing late toxicities for these patients with a good prognosis, low dose radiotherapy is promising as an effective treatment for MZL involving the dura.