S1647
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
structure, custom Plexiglas plates were inserted between torso slices. These contain dedicated slots for optically stimulated luminescence dosimeters (OSLs) and allow insertion of lung- and bone-equivalent materials (cork and plaster) for tissue simulation. Additional cavities accommodate Gafchromic films and ionization chambers for two-dimensional and point-dose verification. Comprehensive OSL calibration measurements were performed to characterize detector performance under different build-up and material conditions.
Conclusion: TrueBeam multi-isocentre VMAT CSI can be accurately and reproducibly delivered. The adopted PSQA protocol includes Delta4 measurement per isocentre (3%/3 mm local γ, >95%), point dose measurement within ±3% and EBT4 film dose plane measurement at 5%/3 mm local γ (>95%) per junction. References: Zhou, Y., Ai, Y., Han, C., Zheng, X., Yi, J., Xie, C. and Jin, X., 2020. Impact of setup errors on multi ‑ isocenter volumetric modulated arc therapy for craniospinal irradiation. Journal of Applied Clinical Medical Physics, 21(11), pp.115-123. Keywords: cranio-spinal VMAT, multi-isocenter, PSQA
Figure 1: Modular Plexiglas plate with OSL cavities integrated into the Alderson phantom (air gap, cork).The influence of Plexiglas build-up, air gaps, irradiation direction, and lung/bone-equivalent inserts was systematically evaluated (Figure 1). Results: OSLs demonstrated linearity up to 10 Gy, with accuracy within ± 5 % and reproducibility better than 1 %. Irradiation direction showed negligible influence on OSL response, supporting flexible placement within the phantom. Plexiglas plates had minimal dosimetric impact (< 4 %), whereas air gaps between slices caused local dose deviations of up to 30 % compared to homogeneous reference setups. Filling these cavities with cork and plaster improved dose uniformity, reducing deviations below 3 %. Both materials were easy to integrate and provided stable readouts. Conclusion: We successfully developed a modified anthropomorphic total-body phantom combining a commercial ART torso with modular extensions. The integration of OSLs, films, and ionization chambers enables complementary high-resolution and absolute dosimetry. Systematic preparatory investigations established detector reliability, material equivalence, and identified air gaps as a key uncertainty source. This modular total-body phantom represents a crucial step toward standardized, quantitative verification of TBI dose delivery across centers, supporting future evidence-based harmonization of TBI practice. References: [1] Shariff M. et al., Large-field irradiation techniques
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Design and Characterization of a Modular Anthropomorphic Phantom for Total Body Irradiation Verification Leon Feldhus, Christoph Bert, Maya Shariff Department of Radiation Oncology, Universitätsklinikum Erlangen, Erlangen, Germany Purpose/Objective: Total body irradiation (TBI) remains a cornerstone in conditioning regimens before stem cell transplantation. In Germany, a wide variety of TBI techniques are in clinical use, as demonstrated by a recent nationwide survey and planning comparison study [1,2]. To provide a robust platform for standardized dosimetric verification across centers, we developed an anthropomorphic total-body phantom. The purpose of this work is to present its design and preparatory dosimetric investigations forming the basis for an upcoming German multicenter verification study and future harmonization of TBI dosimetry. Material/Methods: The phantom is based on the commercially available Alderson Radiation Therapy (ART) phantom. To enable integration of dosimeters without damaging the
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