ULTRA-LOW DOSE RADIOTHERAPY (ULDR) (4Gy) FOR INDOLENT ORBITAL ADNEXAL LYMPHOMAS (IOAL): AN INTERNATIONAL LYMPHOMA RADIATION ONCOLOGY GROUP STUDY

Abstract

Introduction: ULDR is reported to be effective for a range of indolent lymphomas. This is particularly relevant for lymphomas of the orbit where standard radiotherapy doses may be associated with long term sequelae. This large, international retrospective study evaluates the efficacy of 4Gy radiotherapy including outcomes in patient subsets and late toxicity.

Methods: Eligible patients received 4Gy radiotherapy for IOAL at 18 centres between 2006 and 2024. Of 320 patients entered, a preliminary analysis was performed for 270 patients (321 orbits) with complete data available. Freedom from local failure (FFLF) was measured from commencement of radiotherapy (or from date of first response assessment for the landmark analysis). The study met local institutional review board requirements.

Results: The median age at diagnosis of IOAL was 68 years (range 22–97), with 58% females. Histology was marginal zone lymphoma in 66% of orbits and location was conjunctival (solely) in 23%. Radiotherapy was given to the whole orbit in 72% of orbits, conjunctiva only in 19% and other partial orbit volumes in 9%. The median followup was 2.4 years (inter-quartile range 1–4.3). Initial complete and partial response rates (per orbit) were 64% (95% CI: 58–69) and 34% (95% CI: 29–40) respectively, at a median of 72 days following RT. Five-year FFLF was 86% (95% CI: 80–90) for all treated orbits. In a landmark analysis five-year FFLF was 90% (95% CI: 83–95) after an initial CR to radiotherapy, and 83% (95% CI: 73–89) after an initial PR (Figure). Five-year FFLP were 89% (95% CI: 83–93) and 78% (95% CI: 65–87) for marginal zone lymphoma (MZL) and other histologies, respectively; and 86% (95% CI: 80–91) and 84% (95% CI: 71–91) for conjunctiva-only and other subsites, respectively. Symptoms were reported prior to radiotherapy in 91% of orbits. Complete and partial symptom resolution were reported in 70% and 25% of orbits, respectively. Late effects were uncommon and mild, including dry eye in 16% (all grade 1), cataract in 5%, retinopathy in 1% and glaucoma in < 1%.

Conclusion: In a large, multicentre experience of ULDR for IOAL, durable local control and symptom relief were achieved for the large majority of treated orbits, and with no reported long-term sequelae in 80%. This preliminary analysis also suggests numerically superior outcomes for orbits achieving initial CR and for MZL histology. A final analysis of all enrolled patients is pending.

Keywords: radiation therapy; extranodal non-Hodgkin lymphoma; indolent non-Hodgkin lymphoma

No potential sources of conflict of interest.