Speaker
Description
Purpose/Objectives
The transition from recumbent radiotherapy (RT) to upright patient positioning introduces opportunities to reduce costs of RT facilities, enhance patient’s comfort, increase workflow efficiency, and potentially improve dosimetric outcomes 1 . While studies have examined the feasibility and design of upright systems, regular quality assurance (QA) and patient specific QA (PSQA) remain unresolved. The aim of this work was to translate QA of recumbent RT to upright configurations and highlight key modifications needed for accurate dosimetric, mechanical and treatment accuracy verification.
Materials/Methods
Based on a systematic review of QA guidelines for recumbent photon and particle RT 2 , [3], transferable test and required adaptations for upright RT were identified. Key industry experts developing hardware and software solutions were involved in addressing current and emerging upright RT systems, enabling development of realistic clinical framework for both photon and particle RT.
Results
The main findings were: (1) Dosimetric QA procedures for photon and particle RT remain applicable to upright positioning. The absence of gantry rotation and associated angle dependencies simplifies beam generation, delivery, and commissioning, potentially reducing the overall complexity of routine QA. The phantoms can be positioned either on a plate above the chair or mounted on the backrest (Figure 1). Proper characterization of the water phantom entrance window is crucial for basic beam data collection. (2) Mechanical tests must involve verification of all degrees-of-freedom of the chair movement. (3) Comprehensive end-to-end testing of coordinate transformation between in-beam imaging, chair motion and beam delivery is crucial. Imaging coordinates are aligned with chair and follow any chair tilts. Mechanical chair movements follow chair coordinates and must be aligned with fixed beam coordinates (Figure 2). Sophisticated end-to-end phantom must be developed to test the coincidence of the CT-chair isocenter and beam isocenter, and the correct application of shifts and rotations. (4) In case of treatment planning on recumbent CT, validation of coordinate transformation between out-of-room recumbent planning CT and in-room upright image-guidance must be performed. QA of deformable image registration between images of different anatomical position must be integrated. (5) Combination of dosimetric and mechanical test may be required for PSQA.
Conclusion
Dosimetric QA can be easily translated to upright RT. Geometrical accuracy and co-incidence of all coordinate systems poses the largest challenge. Comprehensive end-to-end testing must be developed for essential validation of spatial and dosimetric accuracy, ensuring reliable coordinate alignment and treatment precision across varying chair positions and orientations.
Acknowledgements
The work was performed in scope of UPLIFT Project (EU grant agreement No. 101168955). CTU has a scientific collaboration with RaySearch Laboratories AB.
References
1 L. Volz et al., “Opportunities and challenges of upright patient positioning in radiotherapy,” Sep. 21, 2024, Institute of Physics. doi: 10.1088/1361-6560/ad70ee.
2 E. E. Klein et al., “Task group 142 report: Quality assurance of medical acceleratorsa,” 2009, John Wiley and Sons Ltd. doi: 10.1118/1.3190392.
[3] B. Arjomandy et al., “AAPM task group 224: Comprehensive proton therapy machine quality assurance,” Med Phys, vol. 46, no. 8, pp. e678–e705, Aug. 2019, doi: 10.1002/mp.13622.