Definitive 24 Gy radiotherapy for stage IE gastric MALT lymphoma: large-scale validation of an optimal dose with reduced acute toxicity.

BACKGROUND: Definitive radiotherapy (RT) doses ≥ 30 Gy are traditionally applied for Helicobacter pylori-independent stage IE gastric mucosa-associated lymphoid tissue (MALT) lymphoma, achieving excellent control. Although 24 Gy may offer comparable efficacy with reduced toxicity, high-quality comparative data are limited. This study aimed to compare the efficacy, toxicity, and long-term outcomes of 24 and 30 Gy RT. METHODS: We retrospectively analyzed 202 patients treated with RT for stage IE gastric MALT lymphoma between 2009 and 2023 (24 Gy, n = 74; 30 Gy, n = 128) at a single tertiary institution. Outcomes included complete remission (CR), freedom from treatment failure (FFTF), overall survival (OS), and grade 2 acute toxicity. Statistical methods included Fisher’s exact test, logistic regression, and Kaplan–Meier estimation, with additional technique-adjusted subgroup analyses to account for temporal changes in RT practice. RESULTS: Median follow-up was 55 months (24 Gy, 36 months; 30 Gy, 69 months; p < 0.001). All patients achieved CR, with 94.1% achieving within 6 months. The 5-year FFTF and OS rates were 99.4% and 100%, respectively. Grade 2 acute toxicity was significantly lower in the 24 Gy group (39.2%) than in the 30 Gy group (60.9%; p = 0.003). Nausea (39.6%) and dyspepsia (18.8%) were most common. Multivariable analysis identified higher-dose RT and female sex as independent predictors of toxicity. Only two patients (1.0%) experienced recurrence. CONCLUSION: Given its comparable disease control to 30 Gy and significantly lower acute toxicity, RT at 24 Gy should be considered the standard dose of choice in this setting.