Long-term Update of a Phase 2 Study of Dose-Reduced Radiation in Diffuse Large B-Cell Lymphoma.

Abstract

Purpose/objective(s): Consolidation radiation therapy (RT) is often recommended in diffuse large B-cell lymphoma (DLBCL). The current recommended dose of 30 Gy was established in the pre-rituximab and PET-CT era. We hypothesized that following a complete response (CR) to modern systemic therapy, as determined by PET-CT, a lower dose of RT would be equally effective.

Materials/methods: Patients with DLBCL or primary mediastinal B-cell lymphoma (PMBL) achieving a CR by PET-CT (Deauville 1-3) after ≥4 cycles of R-CHOP or R-EPOCH were eligible. Consolidation RT dose was 19.5-20 Gy. The primary endpoint of the original study was 5-year freedom from local recurrence (FFLR).

Results: From 2010-2016, 62 patients were enrolled. Stage distribution was: I-II (n=49, 79%) and III-IV (n=13, 21%). Bulky disease (≥7.5 cm) was present in 24 patients (39%). Most (n=58, 94%) received R-CHOP. Four cycles were administered to 34% of patients while 66% received 5-6 cycles. Median follow up was 9 years. Overall, 1 patient experienced local recurrence with FFLR of 98% at both 5 and 10 years (95% CI 88-99%). 7 patients progressed outside of the RT field. Progression-free survival and overall survival at 10 years were 77% (95% CI 62-87%) and 80% (95% CI 64-89%), respectively.

Conclusion: Long-term results of this phase 2 study, with a median follow-up of 9 years, did not demonstrate late local failures when patients received ∼20 Gy consolidation RT. A larger (n=240) confirmatory study from the International Lymphoma Radiation Oncology Group evaluating ∼20 Gy of RT after ≥ 3 cycles of chemoimmunotherapy completed accrual in 2023.