S2717
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
0.200 (0.137-0.231) cm in the chest wall positioning (p adj = 0.00935). Other setup errors were not statistically significant after correction between OSMS and CSMA (all p adj > 0.05). OSMS showed a trend of improvement in AP (p = 0.091) and roll (p = 0.075) based on unadjusted tests, which did not remain significant after false discovery rate correction in the tumor bed positioning (all p adj > 0.16).
Conclusion OSMS significantly improves LR and AP setup accuracy under DIBH for both chest wall and tumor bed positioning and particularly reduces AP error under FB for the chest wall positioning. Improvements are primarily observed in translational axes (LR and AP), while rotational errors remain comparable between OSMS and CSMA. Findings support OSMS as a viable alternative to conventional skin mark alignment, particularly under the DIBH condition as it enhances setup accuracy in specific directions for postoperative radiotherapy in patients with breast-conserving surgery. Inter and Intrafraction Reproducibility in HyperArc Stereotactic Radiotherapy: comparison of three immobilization masks. Nicolle Gomes, Tiago Silva, Ana Furtado, João Marques, João Paixão, Maria da Graça Coelho, Carlo Greco Radiotherapy, Champalimaud Foundation, Lisbon, Portugal Purpose/Objective: HyperArc is a high-dose, highly conformal radiotherapy technique that depends on precise and reproducible patient positioning. The QFix Encompass™ immobilization system, designed for frameless stereotactic radiotherapy, integrates with IGRT and Surface SGRT to achieve submillimetric Digital Poster 1862
Fig 1: Setup errors in the DIBH
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