S2733
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
1 Department of Allied Health Professions, Careggi University Hospital, Florence, Italy. 2 Radiation Oncology Unit, Careggi University Hospital, Florence, Italy. 3 Department of Experimental and Clinical Biomedical Sciences “M. Serio”, University of Florence, Florence, Italy. 4 Medical Physics Unit, Careggi University Hospital, Florence, Italy. 5 Health Management Direction, Careggi University Hospital, Florence, Italy Purpose/Objective: Stereotactic body radiotherapy (SBRT) is commonly used in clinical practice to treat upper abdominal targets. Abdominal compression (AC) can be used as a motion management strategy to reduce intrafraction tumour motion. As AC can reduce internal organ motion, it may also affect setup errors when an indexing system is present. This potential impact could be influenced by body mass index (BMI). This study aimed to retrospectively evaluate the reproducibility of the AC device in patients with primary or secondary liver tumors and to assess whether BMI affects the reproducibility and usability of the AC equipment. Material/Methods: In this study, 49 patients treated with SBRT for primary or secondary liver tumors between 2022 and 2025 at a single centre were included. Patients were stratified into two groups based on their BMI (Underweight or Healthy Weight with BMI <25 kg/m ² vs Overweight or Obesity classes with BMI ≥ 25 kg/m ² ). All patients were positioned supine, arms up, with kneefix and AC belt. Daily online-matched cone-beamCTs (CBCTs) were acquired prior to treatment delivery. Initial translational and rotational setup errors for each axis were determined for all patients. Statistical analyses included an F-test to compare variances in setup error and a Wilcoxon–Mann–Whitney test to evaluate differences in average setup error between BMI groups. Results: In total, 23 liver cancer patients were assigned to the high BMI category and 26 to the normal BMI category. A total of 164 CBCTs were reviewed. The mean setup errors along each axis were similar between the two BMI groups, with no statistically significant differences observed for either translational or rotational axes. However, translational shifts greater than 1 cm occurred more frequently in patients with higher BMI (64%), particularly in the lateral direction. Comparison of variance revealed a significant difference (p<.05) between the two BMI groups for all translational axes, as shown in Table 1.Table 1. Comparison of mean setup error and variance between BMI groups (<25 vs ≥ 25 kg/m ² )
Results:
The results are presented in Table 1. The hybrid planner succeeded in finding a collision-free path across all the test cases. The purely deterministic planner succeeded for all the cases originating from the first start position, 23 cases originating from the second start position, 17 cases originating from the third start position, and none of the cases originating from the fourth start position. These findings highlight the flexibility of the hybrid approach in navigating from various room positions to the treatment head area, while maintaining predictable and deterministic movements around the treatment head. Conclusion: The developed hybrid path planning approach helps clinicians to plan movements of patient positioning robots efficiently. The flexible nondeterministic planner computes paths from various positions in the room to the treatment head area. The deterministic planner creates predictable movements in the treatment head area that are favored by clinicians. The algorithm is integrated into the v2025-SPC1 version of RayCommand software and has passed clinical verification tests at MedAustron. References: [1] Kuffner, James J., and Steven M. LaValle. "RRT- connect: An efficient approach to single-query path planning." Proceedings 2000 ICRA. Millennium conference. IEEE international conference on robotics and automation. Symposia proceedings (Cat. No. 00CH37065). Vol. 2. IEEE, 2000.[2] https://www.medaustron.at/en/ (date: 2025- 10- 15)[3] https://www.raysearchlabs.com/raycommand/ (date: 2025-10-15) Keywords: Patient positioning, Radiotherapy robotics Mini-Oral 3015 Optimizing liver SBRT setup: is BMI affecting setup accuracy and reproducibility? Andrea Lastrucci 1,2 , Nicola Iosca 1,2 , Livia Marrazzo 3,4 , Mauro Loi 2 , Valentina Gigli 5 , Letizia Scaglione 1,2 , Michele Aquilano 2 , Gabriele Simontacchi 2 , Alessandra Galardi 2 , Marianna Valzano 2 , Pierluigi Bonomo 2 , Yannick Wandael 1 , Renzo Ricci 1 , Cinzia Talamonti 3,4 , Lorenzo Livi 3,2 , Stefania Pallotta 3,4
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