S2747
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Results: For 40 patients, IVD showed close agreement with planned dose across regions: Head 99.6 ± 0.6%, Thorax 99.4 ± 0.2%, Lumbar 97.1 ± 3.1%, Pelvis 96.8 ± 2.7% (Figure 1).
EPID-based IVD integrated into a CBCT-guided VMAT- TBI workflow is feasible, accurate, and reproducible with closer monitoring and potential adaptation warranted in cases of pronounced swelling. It detects clinically meaningful anatomical changes, enabling targeted review and supporting adaptive decisions in TBI, while maintaining target coverage and respecting OAR constraints. References: [1] Dogan, N., Mijnheer, B. J., Padgett, K., Nalichowski, A., Wu, C., Nyflot, M. J., ... & Greer, P. B. (2023). AAPM Task Group Report 307: use of EPIDs for patient - specific IMRT and VMAT QA. Medical physics, 50(8), e865-e903. [2] Hoeben, B. A., Pazos, M., Seravalli, E., Bosman, M. E., Losert, C., Albert, M. H., ... & Janssens, G. O. (2022). ESTRO ACROP and SIOPE recommendations for myeloablative Total Body Irradiation in children. Radiotherapy and Oncology, 173, 119-133. Keywords: Total body irradiation - In vivo dosimetry - VMAT Digital Poster Highlight 4369 Implementation of an EPID-Based In-Vivo Dosimetry Program Francesca Greco 1 , Maria Vaccaro 1 , Sofia Raponi 1 , Gerardina Stimato 1 , Stefania Teodoli 1 , Andrea Fidanzio 1 , Matteo Galetto 1 , Flavia Tomei 2 , Gabriele Turco 2 , Chiara Elia 2 , Emanuele Gemma 2 , Valeria Debellis 2 , Silvia Chiesa 2 , Elisa Meldolesi 2 , Maura Campitelli 2 , Stefania Manfrida 2 , Vincenzo Frascino 2 , Maria Antonietta Gambacorta 2 , Marco de Spirito 1 1 Department of Radiology and Oncological Radiotherapy, UOC Fisica per le scienza della vita, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy. 2 Department of Radiology and Oncological Radiotherapy, UOC Radioterapia Oncologica, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy Purpose/Objective: Integrating in-vivo dosimetry (IVD) into image-guided radiotherapy enables detection of clinically relevant anatomical or setup variations. An EPID-based IVD program using PerFraction software (Sun Nuclear a Mirion® company) across a high-throughput clinical setting comprising four linacs, in high volume center. This work reports program design, clinical workload, and early performance metrics. Material/Methods: IVD was applied to VMAT treatments of head-and-neck (HN), pelvic/gynecologic, and thoracic/abdominal sites [1]. All patients underwent daily CBCT-based setup verification with 6DOF corrections. Measurements
The measurements in head and thorax regions, were within the 95–105% band, confirming accurate and reproducible delivery. However, IVD measurements in the lumbar and pelvic regions exhibited greater variability, related to changes in arm positioning, patient preparation, and abdominal distension. Two patients showed lumbar/pelvic IVD values outside the 95–105% tolerance band. Daily CBCTs revealed anatomical changes like abdominal distension and different hydration status, due to concomitant pharmacological therapies. These changes were reproduced on the planning CT, and the plan was recalculated to quantify the impact on PTV coverage (V95/V90) and OAR doses (lung/kidney Dmean) [2] for each patient (Fig. 2).
Across the clinically observed range ( Δ s) all variations remained in tollerance: V90/V95 met coverage thresholds and Dmean for lungs and kidneys stayed below limits. Abdominal swelling (+ Δ s) showed a monotonic reduction in coverage approaching thresholds only at larger simulated Δ s, whereas abdominal reduction ( −Δ s) maintained stable coverage. Kidney mean dose was more sensitive than lung, but with minor changes. Conclusion:
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