S2745
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Interest (OOI) dose compared to conventional anatomy-based patient positioning (ABPP). Material/Methods: Fifteen head-and-neck cancer (HNC) patients receiving IMPT between December 2024 and June 2025 were included in this study. Treatment plans were robustly optimized with 3 mm setup and 3% range uncertainty. Prior to each treatment fraction, patients were positioned by aligning the in-room acquired CBCT to the planning CT (pCT) following standard clinical procedures. Prior to the alignment, the CBCT and its position relative to the beam isocenter were exported to determine the optimal treatment isocenter coordinates. The DGPP algorithm converts the CBCT to a synthetic CT (sCT) using a DCNN1 and propagates relevant structures from the pCT to the sCT using deformable image registration. Subsequently, it optimizes the sCT position for target coverage using a GPU-based Monte Carlo (Moqui2) and gradient descent maximizing the V95% of the primary CTV of 70Gy and the elective CTV of 54.25Gy, expanded by 1mm for optimization3. The accumulated dose over all fractions using DGPP was compared to ABPP for primary CTV coverage and NTCP of xerostomia and dysphagia considering dose to the submandibular and parotid glands, oral cavity, and pharyngeal constrictor
E. Fifty-six (56%) patients required at least one repositioning (E: 62%; C:50%, p=0.086). The mean proportion of sessions requiring patient repositioning was significantly higher in E compared with C (6.3% vs. 4.3%; p=0.048). Use of transit regulators, gastrointestinal toxicity, quality of life, weight change, Bristol or SEFI scores were similar in the 2 groups. Conclusion: The study did not show the benefit of an APA and dietetic TPE programs on the rate of repositioning induced by the presence of stool or gas during radiotherapy. The rate of repositioning reported in the study is much lower than previously observed, probably due to a systematic initial oral and written information also to patients in the control arm on the potential benefit of dietary and exercise. Therefore, the study was underpowered to detect any significant advantages of dietary and APA TPE. References: 1. de Crevoisier R, Tucker SL, Dong L, Mohan R, Cheung R, Cox JD, Kuban DA. Increased risk of biochemical and local failure in patients with distended rectum on the planning CT for prostate cancer radiotherapy. Int J Radiat Oncol Biol Phys. 2005 Jul 15;62(4):965-73.2. McNair HA, Wedlake L, Lips IM, Andreyev J, Van Vulpen M, Dearnaley D. A systematic review: effectiveness of rectal emptying preparation in prostate cancer patients. Pract Radiat Oncol. 2014 Nov-Dec;4(6):437-47. Keywords: prostate cancer, education, reproducibility Poster Discussion 4253 BRIDGE project: Dose-guided patient positioning in head-and-neck cancer patients treated with protons Femke Oosterhof, Makbule Atasoyu, Gabriel Guterres Marmitt, Daniele Cannavò, Tirza L. van Faassen, Carol E. McKenna, Pietro Pisciotta, Jeffrey Free, Johannes A. Langendijk, Stefan Both Radiation Oncology, Unversity Medical Center Groningen, Groningen, Netherlands Purpose/Objective: Proton radiotherapy requires accurate patient positioning before each treatment fraction, routinely assessed manually using in-room CBCT based on anatomical features. However, positioning guided by the expected dose distribution may result in more optimal treatment alignment by accounting for anatomical changes, enhancing treatment quality assurance and generating adaptive triggers through daily online dose distributions. The main objective was to test if dose-guided patient positioning (DGPP) did not result in inferior target coverage and Organ of
muscles. Results:
The results for the accumulated dose distribution to the primary CTV is shown in Figure 1. The difference between DGPP and ABPP in the total mean dose to the primary CTV was no greater than 0.1Gy, which is well below the predefined safety threshold of 1Gy. The difference in V95% ranged from -0.2% to 0.4%. The NTCP, shown in Figure 2, remained within 0.6% using DGPP compared to ABPP for all evaluated complications. Conclusion: The results of the BRIDGE study demonstrate that DGPP achieves comparable target coverage and NTCP- values as current standard anatomy-based manual positioning procedure for HNC patients treated with IMPT. Daily fraction-level and longitudinal dose accumulation enable effective treatment monitoring and support timely assessment for plan adaptation. These findings support the feasibility of DGPP, and further research is warranted to enable its clinical adoption.
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