Design and Characterization of a Modular Anthropomorphic Phantom for Total Body Irradiation Verification
Abstract
Purpose
Total body irradiation (TBI) is an essential component of conditioning regimens prior to hematopoietic stem cell transplantation. Recent nationwide comparisons have revealed substantial inter-institutional variability in TBI techniques, highlighting the need for standardized quantitative verification approaches. We developed a modular anthropomorphic total-body phantom to enable reproducible end-to-end verification of TBI dose delivery and present its design and preparatory dosimetric investigations for an upcoming multicenter study.
Methods
The phantom was based on an Alderson Radiation Therapy phantom and extended using custom Plexiglas plates inserted between torso slices. These interfaces enabled reproducible placement of optically stimulated luminescence dosimeters and integration of lung- and bone-equivalent materials using cork and plaster inserts. Additional cavities accommodated Gafchromic films and ionization chambers for two-dimensional dose measurements and absolute point-dose verification. Detector calibration measurements characterized linearity, accuracy, and reproducibility under varying build-up and material conditions. The dosimetric influence of Plexiglas build-up, inter-slice air gaps, irradiation direction, and tissue-equivalent inserts was systematically investigated.
Results
Detectors demonstrated linearity up to 10 Gy, accuracy within 5%, and reproducibility better than 1%, with negligible dependence on irradiation direction. Plexiglas plates caused clinically negligible dose perturbations below 4%. In contrast, air gaps between phantom slices produced pronounced local dose deviations of up to 30% relative to homogeneous reference measurements. Filling these cavities with cork or plaster substantially improved dose uniformity, reducing deviations to below 3%. Gafchromic films enabled high-resolution two-dimensional dose visualization, while ionization chambers provided reliable absolute dose verification.
Conclusion
A modular anthropomorphic total-body phantom was developed for reproducible TBI dose verification. Preparatory investigations identified inter-slice air gaps as the dominant uncertainty source and demonstrated effective mitigation using tissue-equivalent inserts. The phantom provides a robust platform for consistent multicenter TBI verification and supports future harmonization of clinical TBI practice.