Phase 2 Study of Dose-Reduced Consolidation Radiation Therapy in Diffuse Large B-Cell Lymphoma

Abstract

To evaluate the feasibility of reducing the dose of consolidation radiation therapy (RT) in diffuse large B-cell lymphoma. This phase 2 study enrolled patients with diffuse large B-cell lymphoma, not otherwise specified and primary mediastinal (thymic) large B-cell lymphoma in complete response on positron emission tomography-computed tomography imaging after ≥4 cycles of a rituximab/anthracycline-containing combination chemotherapy regimen. Consolidation RT used a dose of 19.5 to 20Gy. The primary endpoint was 5-year freedom from local recurrence. Sixty-two patients were enrolled between 2010 and 2016. Stage distribution was as follows: I to II (n=49, 79%) and III to IV (n=13, 21%). Bulky disease (defined as ≥7.5cm or ≥10cm) was present in 23 (40%) and 16 (28%) patients, respectively. Chemotherapy was R-CHOP (then list the drugs) in 58 (94%) and R-EPOCH (then list the drugs) in 4 (6%) with a median of 6 cycles. With a median follow-up of 51months, 7 patients developed disease progression (6 outside the RT field, 1 within the RT field). Freedom from local recurrence at 5years was 98% (90% lower confidence bound, 88%). Progression-free and overall survival at 5years were 83% and 90%, respectively. With more effective systemic therapy (e.g., addition of rituximab) and more refined chemotherapy response assessment (e.g., positron emission tomography-computed tomography), the dose of RT in combined modality treatment programs may potentially be reduced to 20Gy. This achieves excellent local control with the potential to decrease acute and long-term side effects.