Long-term outcome, relapse patterns, and toxicity after radiotherapy for orbital mucosa-associated lymphoid tissue lymphoma: Implications for radiotherapy optimization

Objectives: Although mucosa-associated lymphoid tissue lymphoma (MALToma) is sensitive to radiation therapy (RT), the optimal RT dose and treatment volumes have not been established. This study aimed to assess the relapse patterns and outcomes of patients with orbital MALToma who underwent RT and to suggest implications for optimized RT. Methods: We reviewed 212 patients (246 orbits) diagnosed with orbital MALToma who received RT between 1993 and 2013. Median RT dose was 25.2 Gy. Generally, conjunctival and eyelid lesions were irradiated with electrons, whereas retrobulbar and lacrimal gland lesions with photons. Lens shielding was used for 70% of treated eyes, mainly conjunctival and eyelid tumors. Results: Relapse occurred in 29 patients. Among 11 patients with local relapse (LR), 4 were attributed to insufficient dose (n = 2) and improper RT volume (n = 2). The 10-year LR, contralateral orbit relapse, and distant relapse rates were 8.6%, 12.8% and 4.9%, respectively. Twelve patients died of disease-specific causes (n = 1) and intercurrent diseases (n = 11). The 10-year relapse-free survival, overall survival, and cause-specific survival rates were 69.7%, 88.2% and 98.8%, respectively. Grade 3 cataracts and nasolacrimal duct obstruction were observed in 27 and 4 orbits, respectively. Conclusion: Low-dose RT with proper lens shielding is an appropriate treatment for orbital MALToma in terms of high disease control rate and acceptable morbidity. However, lower RT dose may be attempted to further reduce toxicity while maintaining excellent outcomes.