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Orbital lymphoma is an uncommon disease, accounting for 10% of all orbital tumours and 1% of non-Hodgkin’s lymphoma. The use of 24Gy over 12 fractions has been proven to be the optimal dose for patients with indolent lymphomas in general, with 4Gy over 2 fractions being useful for palliation in the European population. There is, however, emerging evidence that the use of 4Gy over 2 fractions for indolent orbital lymphomas provides comparable local control and overall survival rates as higher doses. We sought to evaluate and compare the outcomes of an Asian patient population treated with different radiotherapy (RT) regimens for orbital MALT lymphoma.

This was a retrospective cohort study of patients diagnosed with orbital MALT lymphoma from 1999 to 2021 at the National Cancer Centre Singapore. Patients were treated with RT according to their physician’s preference. The endpoints were local control rate (LCR), progression free survival (PFS) and overall survival (OS).

A total of 64 patients were analysed, with a median age of 58 years. The most common tumour location was within the orbital cavity (58%), and 80% of patients had stage 1 disease. A majority of treatments were delivered with a curative intent (88%) using 3D conformal RT (91%). Seven patients received 4Gy (5 of which were for palliation), 39 patients received 24Gy, and the remaining 18 patients received a range of doses from 23.4-35.8Gy in 13-20 fractions. Treatment compliance was high (97%). With a median follow up of 6.4 years, the 5-year LCR, PFS and OS were 96.1% (95% CI 87.9-99.3%), 87.7% (95% CI 74.0-94.4%) and 96.8% (95% CI 87.7-99.2%) respectively. The PFS of patients who received 4Gy vs those who received 24Gy and above were comparable (Hazard ratio [HR]=0.42, 95% CI 0.11-1.53, p=0.173) The OS of patients who received 24Gy was superior to those who received 4Gy (HR=0.10, 95% CI 0.02-0.52, p=0.001), although it is worth noting that the 5yr OS for those who received 4Gy was 100% compared to 96.5% for patients who received 24Gy and above.  Age at diagnosis (HR=1.10, 95% CI 1.03-1.18) and RT duration (HR=0.89, 95% CI 0.82-0.97) were also found to be significantly associated with OS. Exploratory multivariable analysis with adjustment to account for model overfitting suggested that age at diagnosis was the only independent predictor of OS (HR=1.09, 95% CI 1.02-1.17).

This study in an Asian cancer centre showed that RT for orbital MALT lymphoma provided excellent LCR, PFS and OS. Analyses suggested that outcomes of patients treated with 4Gy were comparable with those who received higher doses of 24Gy and above. Hence it would be worth prospectively evaluating these associations in future studies with a larger number of patients.