R. Zou1, A. L. Schwer2, S. V. Dandapani1, J. Y. C. Wong1, A. Amini1, N. Khan3, A. Kallam3, S. Kambhampati3, J. Baird3, A. Borogovac4, G. Shouse3, M. Mei3, A. Herrera3, T. Siddiqi3, L. E. Budde3, Y. J. Chen1, and C. J. Ladbury1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2Department of Radiation Oncology, Lennar Comprehensive Cancer Center, City of Hope National Medical Center, Irvine, CA, 3Department of Hematology and Hematopoietic Cell Transplantation, City of Hope National Medical Center, Duarte, CA, 4Department of Hematology and Hematopoietic Cell Transplantation, Lennar Comprehensive Cancer Center, City of Hope National Medical Center, Irvine, CA
Purpose/Objective(s):Due to randomized data published in the 2010s, the standard of care radiation dose for early-stage indolent non-Hodgkin lymphomas decreased to 24-30.6 Gy. Emerging data suggest that even lower doses (4 Gy) may be reasonable in select cases to limit toxicity, though they are associated with higher rates of disease relapse. However, real-world uptake of these clinical recommendations is unclear. Our study aims to evaluate current practice patterns of radiation treatment for early-stage indolent lymphomas. Materials/
Methods: We conducted a retrospective analysis using the National Cancer Database for patients with stage I-II, grade 1-2 follicular or marginal zone lymphoma diagnosed between 2010-2021. Patients were excluded if they were not treated with radiation, had unknown radiation details, or received concurrent chemotherapy or immune-based therapies. Patients were stratified per the total radiation dosage received into the following groups: 4 Gy, 24-30.6 Gy, 30.7-36 Gy, and 40-45 Gy. Patients receiving doses outside these ranges were excluded. Trends in the choice of dosage were assessed using linear regression and multivariable (MVA) logistic regression. Results: A total of 7517 patients met inclusion criteria, with 238 (3.2%) receiving 4 Gy, 6294 (83.7%) receiving 24-30.6 Gy, 760 (10.1%) receiving 30.7-36 Gy, and 225 (3.0%) receiving 40-45 Gy. 1107 (14.7%) of patients received 24 Gy. There were significant changes over time. In 2010, 0.2% received 4 Gy, 72.0% received 24-30.6 Gy, 22.2% received 30.7-36 Gy, and 5.6% received 40-45 Gy. In 2021, 7.5% received 4 Gy (slope: 0.7%/yr; p<.001), 90.3% received 24-30.6 Gy (slope: 1.7%/yr; p<.001), 1.9% received 30.7-36 Gy (slope: -1.8%/yr; p<.001), and 0.3% received 40-45 Gy (slope: -0.5%/yr; p<.001). When specifically examining the dose of 24 Gy established in randomized trials, there was a significant increase from 1.6% in 2010 to 32.8% in 2021 (slope: 2.7%/yr; p<.001). On MVA, Hispanic patients were significantly less likely to receive the current standard of care dose of 24-30.6 Gy (OR: 0.64; p<.001). Increasing year of diagnosis (OR: 1.14; p<.001), marginal zone histology (OR: 1.78; p<.001), treatment at a facility within 25 miles (OR:1.37; p<0.001) and treatment at a high-volume facility (Ref: >median volume; OR: 1.16; p=.029) were associated with increased probability of receiving 24-30.6 Gy. There was a trend towards increased utilization of 24-30.6 Gy at community hospitals (Ref: academic; OR: 1.42; p=.055). Conclusion: Consistent with currently available data and guidelines, practice patterns have adapted to treat the vast majority of patients with early-stage indolent lymphoma to a dose of 24-30.6 Gy, with 4 Gy also being increasingly used in select cases. Our analysis also revealed that socioeconomic factors influenced the receipt of standard-of-care dosing. Further work is warranted to identify and address potential barriers to the clinical implementation of radiotherapy dosing consistent with the standard of care.
