Salvage ultra-low-dose radiotherapy for conjunctival mantle cell lymphoma - a case report and literature review.

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma with variable responses to frontline chemotherapy. Orbital involvement is rare, and data on radiotherapy, particularly at ultra-low doses, remain limited. The authors report a 64-year-old male with conjunctival MCL refractory to a single cycle of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone). He underwent salvage ultra-low-dose radiotherapy (VLDRT; 4 Gy in 2 fractions) to the left orbit using volumetric modulated arc therapy (VMAT) with 6 MV photons, daily cone beam computed tomography (CBCT) image guidance, thermoplastic mask immobilization, and a 0.5 cm bolus. The patient achieved significant clinical improvement and complete metabolic response within weeks. Ophthalmology evaluation documented preserved visual acuity, normal fundoscopy, and no toxicity. At 24 months, orbital remission is maintained, despite later systemic relapse managed with R-DHAOx regimen (rituximab, dexamethasone, high-dose cytarabine, and oxaliplatin) and ibrutinib, achieving systemic control while maintaining orbital remission. VLDRT can provide durable local control and functional preservation in anatomically critical sites. This case, together with recent literature, highlights the potential role of VLDRT as a salvage strategy in aggressive lymphomas.