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 20 Gy. 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 ≥7.5 cm or ≥10 cm) 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 51 months, 7 patients developed disease progression (6 outside the RT field, 1 within the RT field). Freedom from local recurrence at 5 years was 98% (90% lower confidence bound, 88%). Progression-free and overall survival at 5 years 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 20 Gy. This achieves excellent local control with the potential to decrease acute and long-term side effects.