Efficacy of low dose radiotherapy for primary orbital marginal zone lymphoma

Marginal zone lymphoma (MZL) is a radiosensitive tumor, with high local control (LC) rates with moderate dose radiotherapy (RT). This retrospective study, performed at the Peter MacCallum Cancer Centre, evaluated the efficacy and toxicity of patients with orbital MZL treated to 24-25 Gy. Twenty-four patients (27 orbits) were identified, with median follow-up of 41 months. Disease was conjunctival in 16 orbits (59%), lacrimal in seven (26%), in the eyelid in one (4%) and elsewhere in three (11%). All patients attained a complete response. Three patients had treatment failures: one local relapse, one contralateral and one distant relapse. Freedom from local failure, freedom from progression, progression-free survival and overall survival were 100%, 90%, 90% and 100% at 2 years and 92%, 81%, 81% and 100% at 5 years, respectively. Aside from cataractogenesis, there was no significant late toxicity. Our study shows that RT doses of 24-25 Gy provide high rates of LC for orbital MZL with acceptable morbidity.