S2114
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
between nominal 6DOF couch rotations and SGRT reported measurements were 0.1° for both roll and pitch with no detectable discrepancy in yaw. End-to- end tests were satisfactory across all components. For imaging coincidence between SGRT and CBCT measurements, there was a post translational shift maximum discrepancy of 0.9 mm in the vertical axis and 0.20° in the pitch and yaw axes (Figure 2).Figure 1. Shift localization accuracy of SGRT vs. nominal couch shifts.
Conclusion: The O-ring SGRT system was deemed to be clinically satisfactory with TG-302 tolerances and recommendations. Translational localization accuracy and reproducibility was found to be within the TG-302 criteria of < 1mm, when repeatably measured without and with shifts. Imaging coincidence was also within the <1mm TG-302 tolerance, after applying clinically relevant shifts. Finally, rotational localization accuracy was found to fluctuate < 0.3° and differ <0.1° from nominal couch measurements and <0.20° from CBCT image-based measurements. References: References:1. Alexander, D.A., Majji, S., Jermyn, M., Byrd, B.K., Bruza, P., Li, T. and Zhu, T.C., 2023. Characterization of Cherenkov imaging parameters and positional constraints on an O-ring linear accelerator. Physics in Medicine & Biology, 68(20), p.20NT02.2. Al - Hallaq, H.A., Cerviño, L., Gutierrez, A.N., Havnen - Smith, A., Higgins, S.A., Kügele, M., Padilla, L., Pawlicki, T., Remmes, N., Smith, K. and Tang, X., 2022. AAPM task group report 302: surface - guided radiotherapy. Medical physics, 49(4), pp.e82-e112 Keywords: SGRT, O-ring Halcyon Linac, Surface- guidance Library plan-of-the-day radiotherapy for muscle- invasive bladder cancer: the impact of bladder and rectal filling on replanning. Tommi Leijstra, Kim Compagner, Kasper Schutten, Tristan van Heijst, Rik Westendorp, Djoeri Lipman Radiotherapy, Isala, Zwolle, Netherlands Purpose/Objective: Muscle-invasive bladder cancer (MIBC) can be treated with (chemo)radiotherapy as a bladder-preserving alternative to radical cystectomy. At our institution, a library plan-of-the-day (PotD) approach is applied. Based on full- and empty-bladder planning CT scans (pCT), the bladder is contoured and clinical target volumes (CTVs) are generated by interpolation in the RayStation treatment planning system using scripting. In unifocal bladder cancer, the tumor location is Digital Poster 954
Figure 2. Measured discrepancies between CBCT- and Identify-measured offsets.
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