Clinical Outcomes and Safety of Ultra-Low-Dose Radiotherapy for Ocular Adnexal Lymphoma: A Systematic Review

Background/Objectives: Ultra-low-dose radiotherapy (ULD-RT), an ultra-low-dose regimen delivering 4 Gy in two fractions, has emerged as a promising treatment for indolent ocular adnexal lymphoma (OAL), offering disease control with minimal toxicity. However, the clinical outcomes and safety profile of ULD-RT remain inconsistently reported across studies. Methods: We conducted a systematic review of peer-reviewed studies evaluating ULD-RT in patients with OAL, including prospective, retrospective, and comparative cohorts published between 2000 and 2025. A comprehensive search was performed in PubMed, Embase, and Scopus. Eligible studies reported clinical outcomes (e.g., response rates, local control, progression-free survival) and safety data (acute and late toxicities). Methodological quality was assessed using the Newcastle-Ottawa Scale (NOS). Results: Ten studies comprising 591 patients met the inclusion criteria. The overall response rate to ULD-RT ranged from 88% to 100%, with complete response rates of 50% to 95%. Local control rates ranged from 63% to 100%, and 2-year progression-free survival exceeded 85% in most studies. Importantly, no grade ≥ 3 toxicities were observed following the regimen of 4 Gy in two fractions. Acute toxicities occurred in up to 42% of patients, typically grade 1 dry eye or conjunctivitis. Late toxicities were uncommon (16-33%), with cataracts rarely requiring surgery. All included studies were rated as good quality (NOS score ≥ 7), indicating low risk of bias. Conclusions: ULD-RT is a highly effective and safe treatment modality for OAL, providing excellent local control with a favorable toxicity profile. These findings support the adoption of ULD-RT as a first-line radiotherapy strategy for indolent OAL. Future prospective trials with longer follow-up and standardized toxicity reporting are warranted to confirm and refine its clinical role.