End-to-end technical validation of multi-isocenter total body irradiation using an anthropomorphic phantom

The objective of this study is to perform an end-to-end (E2E) technical validation of a total body irradiation (TBI) workflow using an anthropomorphic phantom, integrating simulation, treatment planning, patient-specific quality assurance, and phantom-based dosimetry to ensure accurate and reproducible dose delivery. A full E2E test was performed using the Rando Phantom and Varian Eclipse TPS. CT scans were acquired in head-first supine (HFS) and feet-first supine (FFS) orientations and registered to simulate full-body imaging. Treatment plans were optimized for both orientations, with specific gradient dose regions defined for overlap zones. ArcCHECK and OSLDs were used for pre-treatment and phantom-embedded dosimetric verification, respectively. Cone Beam CT (CBCT) assessed positional accuracy across eight treatment fractions. Dose discrepancies and alignment errors were evaluated across anatomical regions. HU comparison between the CT console and TPS revealed only minor deviations, all within ± 6 HU, supporting the consistency of HU representation in the TPS. Gamma passing rates exceeded 97% across most regions. OSLD dose differences remained within ± 2.5% for most sites, except thorax and overlap zones, which reached ± 4.8%. CBCT-based setup verification demonstrated sub-millimeter alignment deviations across fractions, indicating consistent positional accuracy. E2E validation using the Rando Phantom supports technical accuracy and consistency in the TBI workflow. Notable dose variations in overlap and heterogeneous regions highlight the need for enhanced QA in complex geometries. The findings support the technical feasibility and reproducibility of the workflow, while further patient-specific and motion-inclusive studies are required to establish broader clinical applicability.