TOPLINE:

Increasing radiation dose from 4 Gy to 8 Gy in two fractions for indolent B-cell lymphomas was associated with better local control and higher complete response rates, although follow-up was shorter in the 8 Gy cohort. Local progression occurred in 26% of sites treated with 4 Gy compared with 7% of those treated with 8 Gy, and the 1-year complete response rate was 81% with 8 Gy compared with 57% with 4 Gy.

METHODOLOGY:

• While 4 Gy in two fractions has grown in use for indolent B-cell lymphomas, local progression can occur in 30% of patients.
• To assess whether increasing radiation dose to 8 Gy in two fractions could improve cancer control, researchers conducted a retrospective review of 121 patients with indolent lymphoma at a single institution in the US between 2013 and 2024.
• Patients with diagnoses of follicular lymphoma, marginal zone lymphoma, or unspecified low-grade B-cell non-Hodgkin lymphoma were included. Overall, a total of 77 sites of disease in 68 patients were treated with 4 Gy in two fractions, while 60 sites in 53 patients received 8 Gy in two fractions.
• Local control and complete response were primary endpoints, assessed using imaging studies such as PET or CT scans and clinical examination.
• Median follow-up was 6.6 years for the 4 Gy cohort and 2.0 years for the 8 Gy cohort.

TAKEAWAY:

• The 1-year cumulative incidence of complete response was 57.4% for the 4 Gy group and 81.4% for the 8 Gy group, with 8 Gy being associated with a higher likelihood of complete response (hazard ratio [HR], 0.54; P = .001).
• On univariate analysis, sites treated with 4 Gy were significantly more likely to recur locally than sites treated with 8 Gy (HR, 2.97; P = .044).
• For nodal sites, treatment with 4 Gy was associated with a fivefold higher likelihood of local recurrence than treatment with 8 Gy (HR, 5.02; 95% CI, 1.08-23.40). On multivariable analysis, nodal site of disease and treatment with 4 Gy were independently associated with a higher risk for local recurrence.
• Larger tumors were more likely to recur, with each 1-cm increase in tumor size associated with a higher risk for local recurrence (HR, 1.14) and a lower likelihood of complete response (HR, 0.92).

IN PRACTICE:

“These early results demonstrate promise that increasing the dose from 4 Gy to 8 Gy improves treatment efficacy while maintaining the advantages of two fractions for indolent B-cell [non-Hodgkin lymphoma],” the study authors wrote.

SOURCE:

The study, led by Jessica F. Burlile, Department of Radiation Oncology, Mayo Clinic in Rochester, was published online on March 16 in Radiotherapy and Oncology.

LIMITATIONS:

The study has a comparatively shorter follow-up time for the 8 Gy arm (2.0 years) compared with the 4 Gy arm (6.6 years), which warrants caution when comparing the two regimens. Sites treated with 8 Gy were treated more recently, while sites treated with 4 Gy were largely treated before 2020, introducing potential temporal bias. The anatomic site distribution was imbalanced between the two groups, with orbital lymphomas comprising 46% of those in the 4 Gy group compared with only 2% of those in the 8 Gy group. Additionally, the largest dimension of the gross tumor volume was greater in the 8 Gy vs 4 Gy group (median, 3.5 cm vs 2.3 cm), which could confound comparisons. Toxicity was not formally assessed as it holds limited validity in the retrospective setting.

DISCLOSURES:

Randa Tao disclosed receiving an honorarium from Total Health for speaking at the Best of ASCO continuing medical education conference. All remaining authors reported having no conflicts of interest. No funding sources were declared for this study.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.