A 20-Gy consolidation radiation dose maintained strong local control in patients with diffuse large B-cell lymphoma (DLBCL) and high-grade B-cell lymphoma (HGBL) who achieved a complete response after chemoimmunotherapy, according to results of an international phase 2 study.

At 3 and 5 years, the rates of freedom from local recurrence were 98.7% and 97.4%, progression-free survival rates were 91.7% and 87.2%, and overall survival rates were 96% and 92.3%, respectively.

“Reducing the dose of consolidation radiation from 30 Gy to 20 Gy did not compromise local control, even in a diverse group of patients,” said study lead author Christopher Kelsey, MD, of Duke University Medical Center, Durham, North Carolina, during the American Society for Radiation Oncology (ASTRO) 2025 Annual Meeting in San Francisco.

Consolidation radiation has long been used in DLBCL and HGBL, particularly for patients with bulky or bone involvement. The 30-Gy standard was set before rituximab and before PET-CT was used to confirm complete response. A 2019 single-center study from Duke suggested 20 Gy could work just as well, prompting this multicenter trial.

Methods and Results

The phase 2 International Lymphoma Radiation Oncology Group study enrolled 243 patients with stages I-IV disease across 16 institutions in the US, Asia, and Europe. All had received at least three cycles of an anthracycline- and rituximab-based regimen and achieved a PET-confirmed complete response. Patients were treated with involved-site radiation therapy (RT) of 19.5-20.0 Gy in 1.5-2.0-Gy fractions.

Most patients (81%) received rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone; 8% received rituximab, etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin; and 11% received other regimens. Seventy-five percent were treated using intensity-modulated or volumetric-modulated arc therapy, 19% with three-dimensional conformal RT, and 6% with proton therapy.

After a median follow-up of 3.1 years, only 16 relapses occurred (one local, three local plus distant, and 12 distant only).

Because a randomized phase 3 trial would require a very large sample, it was deemed impractical, Kelsey said. Still, when viewed alongside the earlier 62-patient Duke series showing 98% local control at 10 years, these results support 20 Gy as a reasonable consolidation dose for patients who achieve a complete response.

‘20 Gy Is Probably Better Than Nothing’

John P. Plastaras, MD, PhD, of the Hospital of the University of Pennsylvania, Philadelphia, agreed that the findings are useful for tumor-board decisions. 

“It’s a tumor-board kind of discussion — case by case — but now we finally have data to inform those conversations,” he told Medscape Medical News.

Plastaras said the results could also reassure medical oncologists.

“If someone shows me that 20 Gy in a single-arm study isn’t associated with worse outcomes, I’m on board. The practical standard right now often ends up being no radiation at all, so 20 Gy is probably better than nothing.”

Kelsey reported consulting for Johnson & Johnson and Colgate-Palmolive Co.
Plastaras reported receiving honoraria from IBA Proton Therapy for advisory-board service.