S2918
RTT- RTT operational practice and workflow innovations
ESTRO 2026
patients completed the MRI treatment planning scan without interruptions or sedatives. Simulation prior to scanning is a promisingmethod to improvebothcomfor t andscan feasibility,and the projectwillcontinue to accrue. Keywords: MRI-simulation, head-and-neck cancer, 3D- print Digital Poster 2152 Optimising Re-imaging Strategies in Image-Guided Radiation Therapy: A Quality Improvement Initiative for Gynaecological Oncology Yixin Jeannie Lin, Lele Tan, Jie Min Clairene Chng, Semaya Natalia Chen Division of Radiation Oncology, National Cancer Centre Singapore, Singapore, Singapore Purpose/Objective: Image-guided radiation therapy (IGRT) enhances treatment precision by improving target accuracy, enabling higher tumour doses than previously achievable. IGRT provides improved visualisation that allows for timely correction, enabling daily adaptive treatment. Whilst this increases treatment accuracy, it requires re-imaging upon correction and consequently, additional radiation exposure due to re- imaging. By establishing clear purposes for re-imaging, overall clinical workflow and patient care delivery can be enhanced. Material/Methods: This study was done retrospectively, using data from 275 gynecological cancer patients who underwent radiotherapy from March 2023 to December 2024. 192 patients had weekly cone-beam computed tomography (CBCT) while remaining 83 patients had daily CBCT. 2473 CBCTs were analysed for re-imaging. Re-imaging factors were classified as setup error, incorrect bladder/rectal filling, internal anatomical changes, machine error, and others.Secondary analysis examining the dosimetric impact of rectal filling variation (original versus gas-distended rectums) was also conducted on 10 patients. To simulate a gas- distended rectum in the treatment plan, the original rectum was assigned to air density and recalculated. Two-tailed paired t-test (p<0.05) was used for statistical analysis. Results:
57% of the patient cohort required repeated CBCT during their treatment. The occurrence of re-imaging was 56% in the weekly CBCT group and 59% in the daily CBCT group, demonstrating that re-imaging is a significant clinical problem. Incorrect rectal filling contributed to the highest incidence of repeat CBCT (n=332, 54%) (Figure 1). Statistical analysis revealed significant differences in rectal dose parameters with air correction. Rectum Dmax increased from 50.95±3.20 Gy to 51.70±3.55 Gy (p= 0.018), and Dmean increased from 37.40±6.43 Gy to 37.92±6.40 Gy (p< 0.01) (Table 1). Despite statistical significance, the small incremental magnitude suggests they are clinically insignificant. Conclusion: Assessing re-imaging rates and their causes, help to identify improvements to reduce patient doses and enhance workflow efficiency. Incorrect rectal filling was identified as the most common factor for re- imaging. Despite routine instructions for patients to empty their rectum before treatment, precise control of rectal volume remains unachievable due to inherent physiological limitations. Based on the results, an improved CBCT assessment protocol has been developed, accepting gas-distended rectum if it remains within the original rectum contour. The updated protocol is designed to decrease the
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