ESTRO 2025 - Abstract Book

S4141

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

ESTRO 2025

Range in the variation between the match values are highlighted in figure 1, with clinical acceptance and comments received reported in table 1. Initial matches scored a similar level of agreement when reported as clinically acceptable (78%, 86% and 74%), requiring advice (16%, 14%, 14%) or not clinically acceptable (6%, 0%, 12%). Image verification results highlighted slightly more variation in levels of agreement. Rectal volume in the PTV and coverage of the PTV were reasons of concern most frequently reported. Conclusion: Our initial investigations demonstrate CBCT soft tissue matching to the urethra is feasible. The findings from this study are currently being used to develop a training package to educate RTTs in the clinical setting.

Keywords: Prostate SBRT, Urethral CBCT Matching

References: Leeman JE, Chen YH, Catalano P, Bredfeldt J, King M, Mouw KW, et al. Radiation Dose to the Intraprostatic Urethra Correlates Strongly With Urinary Toxicity After Prostate Stereotactic Body Radiation Therapy: A Combined Analysis of 23 Prospective Clinical Trials. Int J Radiat Oncol Biol Phys. 2022;112(1):75-82.

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Digital Poster Data-driven optimization of tolerance thresholds in surface-guided radiotherapy for pelvic cancers Wim Vingerhoed, Laura van den Abbeelen, Jolien Cleijman Radiotherapy, Iridium Netwerk, Antwerp, Belgium Purpose/Objective: Intrafraction motion during radiotherapy can compromise treatment accuracy and effectiveness. Surface-guided radiotherapy (SGRT) systems monitor patient positioning and interrupt the treatment beam when deviations exceed preset thresholds. This study aimed to optimize these thresholds, balancing treatment precision and efficiency for pelvic cancer patients. Material/Methods: A retrospective analysis of 1,367 radiotherapy sessions involved 21 gynaecological (469 sessions) and 44 prostate cancer patients (898 sessions). Real-time SGRT data captured positional deviations in six degrees of freedom: lateral, longitudinal, vertical, roll, pitch, and yaw. Deviation patterns were evaluated using cumulative frequency histograms, with manufacturer-standard thresholds as the baseline. Optimized thresholds encompassed 95% of observed deviations, reducing unnecessary beam interruptions while maintaining geometrical accuracy.