Ultra-low dose radiation therapy for primary cutaneous indolent B-cell lymphomas

BackgroundPrimary cutaneous follicle centre lymphoma (PCFCL) and primary cutaneous marginal zone lymphoma (PCMZL) are indolent radiosensitive lymphomas, with national guidelines recommending 24 Grey (Gy) in 12 fractions, despite shorter regimens showing no difference in overall survival. Multiple studies demonstrate 4 Gy in two fractions is effective in other indolent lymphomas. Shorter regimens may result in less toxicity for patients.ObjectivesWe aim to characterise local control rates in PCFCL and PCMZL treated with radiation therapy (RT) with 4 Gy in two fractions.MethodsFrom a single institution database, we retrospectively identified all patients with PCFCL and PCMZL treated with 4 Gy in two fractions between 2011 and 2022. Prior topical or systemic treatments were permitted. T-cell or high-grade B-cell cutaneous lymphomas, or those with less than 6 months follow-up, were excluded. Primary outcomes were rates of response and local failure per lesion as determined by a radiation oncologist and oncologic dermatologist.ResultsForty-three consecutive patients with 98 lesions treated were identified. Twenty-four (56%) of the patients had PCMZL, and the remainder had PCFCL. Most lesions (97%) received RT with electrons. The complete response or partial response rate was 94%. Six local failures were identified (6%). With a median follow-up of 2.75 years, 1-, 2- and 3-year local failure-free survival were 94%, 94% and 92%, respectively. There was minimal acute toxicity, no late toxicity and no cosmesis issues. No clinical features were predictive of local failure.ConclusionsUltra-low dose radiation was associated with high rates of local control and minimal toxicity and may reduce personal burden and financial toxicity in appropriately selected patients.