2212 - Volumetric Modulated Arc Therapy (VMAT) for Total Body Irradiation (TBI): Dosimetric Outcomes and Clinical Feasibility in a Single-Center Experience

Purpose/Objective(s): To evaluate the dosimetric outcomes, clinical feasibility, and toxicity of VMAT for total body irradiation as an alternative to conventional techniques.

Materials/Methods: This retrospective study analyzed nine patients treated with VMAT-TBI from January 2019 to December 2024 in our institution. The cohort included three adults and six pediatric patients undergoing conditioning before hematopoietic stem cell transplantation. Treatment planning consisted of multi-isocenter VMAT from head to mid-femur, while 3D radiotherapy (3DRT) was employed for the lower extremities. Patients underwent head-first and feet-first CT scans for precise setup, with isocenters placed accordingly. Tattoos were used in 8 ptes and SGRT in 1. The most frequent fractionation regimens were 4 Gy in 2 fractions and 12 Gy in 6 fractions (delivered twice daily). Median follow-up was 68 months. Dosimetric parameters, treatment time, and toxicity data were collected and analyzed.

Results: The number of isocenters ranged from 4 to 10 depending on patient height. The mean PTV D98% was 94.4% (range: 91.3%-96.5%). Lung mean dose was 2.97 Gy (range: 2.15-7.21 Gy), with a mean lung dose rate of 0.51 Gy/min (range: 0.2-1.2 Gy/min). Gonadal sparing was achieved when clinically indicated. Acute toxicities were minimal, with seven patients experiencing grade 1 nausea or asthenia. Treatment delivery, including patient setup, was completed in under 100 minutes for most cases. At the last follow-up, eight patients remained alive.

Conclusion: VMAT-TBI is a feasible and reproducible technique with effective dose modulation, allowing for organ-at-risk sparing while maintaining PTV coverage. The workflow optimization achieved in our center enabled rapid treatment delivery with minimal toxicity, demonstrating VMAT-TBI as a viable alternative to conventional total body irradiation.