C. Hui1, E. A. Simiele2, Y. Lozko3, M. S. Binkley1, R. T. Hoppe1, N. Kovalchuk4, and S. M. Hiniker1; 1Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 2University of Alabama Birmingham School of Medicine, Birmingham, AL, United States, 3Stanford Cancer Institute Palo Alto, Palo Alto, CA, 4Department of Radiation Oncology, Stanford University, Stanford, CA
Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) allows for greater organ sparing with improved target coverage compared to 2D total body irradiation (TBI). However, it is unknown whether improved organ sparing translates to a decrease in clinically observed toxicities, and whether these toxicities are significantly different compared to the 2D technique. We aimed to compare differences in toxicities among patients treated with TBI utilizing volumetric modulated arc therapy and 2D total body irradiation (2D-TBI). Materials/
Methods: We performed a matched-pair single institution retrospective analysis for 200 patients treated with TBI from 2014 to 2023. Patient and disease characteristics, treatment details, outcomes and toxicities, using the common terminology criteria for adverse events v5, were collected. Overall survival (OS) and disease-free survival (DFS) were analyzed using the Kaplan-Meier method and compared using log-rank tests, calculated from the time of completion of radiation therapy. Differences in characteristics and toxicities between the VMAT and 2D cohorts were compared using Fisher’s exact test. Results: Of the 200 patients analyzed, 100 patients underwent VMAT-TBI, and 100 patients underwent 2D-TBI. Median age of the entire cohort was 15.2 years, 56% were male, 71.5% had a malignant disease diagnosis, and median follow up time was 19.4 months for patients who were alive. Both median OS and RFS for the entire cohort was not reached. In the VMAT versus 2D group, the 1-year OS was 84.5% (95% confidence interval [CI] 76.6-92.4) versus 84.0% (95% CI 76.8-91.2; p=0.9) and 1-year RFS was 85.2% (95% CI 77.6-92.7) and 80.0% (95% CI 72.1-87.8; p=0.5), respectively. For VMAT TBI, lungs, kidneys, and lenses were spared to 60.6±5.0%, 71.0±8.5%, and 90.1±3.5% of prescription, respectively. For 2D TBI, only lungs were spared using partial-transmission lung blocks for myeloablative regimens. For patients who underwent a myeloablative regimen, the rates of G3+ pneumonitis were also significantly lower, with 0% in the VMAT-TBI cohort versus 11% in the 2D-TBI cohort (p<0.01). Conclusion: The use of VMAT-TBI led to lower dose to organs at risk when compared to the 2D-TBI cohort, which translated to lower rates of mucositis, pneumonitis, and renal toxicities in patients, while maintaining excellent disease control.
