ESTRO 2025 - Abstract Book

S4110

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

Purpose/Objective: Surface-guided radiation therapy (SGRT) has emerged as a promising non-invasive alternative to conventional image-guided radiation therapy methods. This study aimed to evaluate the accuracy and reliability of SGRT compared to cone-beam computed tomography (CBCT) for patient positioning during deep inspiration breath-hold (DIBH) hypofractionated radiotherapy in patients with left-sided breast cancer. Material/Methods: A retrospective analysis was conducted on patients with breast cancer who underwent hypofractionated radiotherapy with DIBH technique. Patient positioning was performed using both SGRT and CBCT systems. The accuracy of SGRT was assessed by comparing 6-degree-of-freedom values with CBCT couch positions as reference of tumor bed PTV (planning target volume). Single measurements were obtained for each degree of freedom following SGRT-guided positioning. Results: Analysis of positioning data showed mean differences (±standard deviation) between SGRT and CBCT measurements of 0.3±2.0 mm (vertical), -0.6±3.3 mm (longitudinal), and -0.6±3.3 mm (lateral) for translational movements among 68 treatment fractions. For rotational movements, differences were 0.29±1.04° (pitch), - 0.08±1.54° (roll), and 0.83±1.41° (yaw). While most of the measurements fell within established clinical tolerances, deviations were noted primarily in the lateral direction. Outlier accounted for 16% (11 of 68) for acceptable positioning accuracy 5 mm for translations and 3° for rotations. Conclusion: While SGRT demonstrated some potential as an alternative to CBCT for patient setup verification in DIBH radiotherapy, this study indicates that its current accuracy falls short of clinical expectations. These limitations suggest that both SGRT technology and patient setup procedures need further refinement and validation before SGRT can reliably replace CBCT in clinical practice. Challenges remain in achieving consistent alignment within established positioning tolerances for patients with left breast cancer undergoing DIBH radiotherapy.

Keywords: SGRT; Patient positioning; Breast radiotherapy

References: 1. Lee SK, Huang S, Zhang L, et al. Accuracy of surface ‐ guided patient setup for conventional radiotherapy of brain and nasopharynx cancer. Journal of Applied Clinical Medical Physics 2021;22:48-57. 2. Sarkar B, Munshi A, Ganesh T, et al. Rotational positional error corrected intrafraction set ‐ up margins in stereotactic radiotherapy: A spatial assessment for coplanar and noncoplanar geometry. Medical Physics 2019;46:4749-4754. 3. Rudat V, Zhao R, Wang B, et al. Impact of deep inspiration breath hold, surface-guided radiotherapy, and daily cbct on the organs at risk in breast cancer radiotherapy. Scientific Reports 2024;14:27814.

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Digital Poster Feasibility of RTT-led CBCT-guided online adaptive radiotherapy for prostate cancer with pelvic lymph node regions Nienke Losekoot, Suzan Gerrets, Marloes Frantzen-Steneker, Wouter Vogel, Jan Jakob Sonke, Peter Remeijer, Zeno AR Gouw Department of Radiation Oncology, The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, Netherlands