ESTRO 2025 - Abstract Book

S4066

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

ESTRO 2025

Purpose/Objective: Total Marrow Irradiation (TMI) is an advanced intensity-modulated radiotherapy technique evolution of Total Body Irradiation (TBI), designed to selectively target bone structures while sparing surrounding healthy tissues. Delivering TMI is complex due to prolonged treatment times and the need for multiple isocenters, making a robust and reliable patient repositioning system essential. Radiation Therapy Technologists (RTTs) play a pivotal role in selecting and implementing effective positioning and immobilization strategies to ensure reproducibility, minimize errors, and protect organs at risk (OAR). This study evaluates the effectiveness of a new in-house repositioning system by analyzing shifts and rotations needed to achieve optimal agreement between Cone Beam Computed Tomography (CBCT) and simulation CT. Material/Methods: Twenty-five patients undergoing TMI from 2023 were analyzed and compared to 88 treated with the previous system. Immobilization utilized a customized frame incorporating thermoplastic masks for the head-shoulders, thorax-abdomen, and legs. RTTs optimized the setup by adapting techniques to improve patient comfort and stability, positioning the arms along the frame and feet within custom-made pillows. To cover the entire body, 7–9 isocenters were required for each patient, with CBCT imaging performed at each isocenter, resulting in 187 CBCT datasets. Translational and rotational errors were measured and compared to historical data using Student's t-test to determine statistical significance.

Results: The mean online translational error is 5.6±8 mm (vertical: 3±3 mm; longitudinal: 2±8 mm; lateral: 3±3 mm), and rotational errors are pitch=0.5±0.8°, roll=0.3±0.6°, yaw=0.4±0.5°. The new repositioning system significantly reduced vertical and lateral shifts compared to the previous system (p < 0.05), demonstrating improved setup accuracy. Standard deviations have also decreased: vertical from 0.6 to 0.34 mm (-43.3%) and lateral from 0.4 to 0.26 mm(- 35%) demonstrating a lower dispersion of values Conclusion: The in-house developed repositioning system significantly reduces patient positioning errors, enhancing the precision and safety of TMI treatments. This work underscores the critical role of RTTs in evaluating and implementing optimal positioning and immobilization strategies. Their expertise ensures patient comfort, reproducibility, and the safe delivery of therapy, particularly for a population where accuracy is essential to achieve therapeutic outcomes while minimizing OAR exposure. This study is supported by grant AuToMI (GR-2019-12370739 funded by the Italian Ministry of Health)