Optimizing low dose radiotherapy for indolent lymphomas: comparing 8 Gy in 2 fractions to 4 Gy in 2 fractions.

BACKGROUND AND PURPOSE: 4 Gy in 2 fractions has grown in use for indolent B-cell lymphomas because of its tolerance and convenience. However, local progression occurs in 30% of patients. In 2020, we introduced 8 Gy in 2 fractions with the hypothesis that this would improve control compared to 4 Gy in 2 fractions.

MATERIALS AND

METHODS

We conducted a retrospective review of 121 patients (137 sites) with indolent lymphoma treated with either 4 Gy or 8 Gy in two fractions between 2013 and 2024 at a single institution. Local control and complete response were primary endpoints, assessed using imaging and clinical exam. Competing-risks analysis and Cox models were applied.

RESULTS

Median follow up for the overall cohort, 4 Gy cohort, and 8 Gy cohort was 2.9 years, 6.6 years, and 2.0 years respectively. Local progression occurred in 26% of sites treated with 4 Gy versus 7% with 8 Gy, and after appropriate censoring via univariate analysis, local control was superior with 8 Gy (HR 2.97, p = 0.044). Complete response at one year was also higher with 8 Gy (81%) than 4 Gy (57%) (HR 0.54, p = 0.001). On multivariable analysis, nodal sites of disease were independently associated with a higher rate of local recurrence, regardless of dose (HR 3.33, 1.13-8.86, p = 0.016).

CONCLUSION

Increasing the dose from 4 to 8 Gy was associated with a higher rate of local control while maintaining the convenience of 2 fractions. Further maturation of this data and results of ongoing prospective studies are needed.