ESTRO 2024 - Abstract Book

S129 ESTRO 2024 of RT. All pioneering heavy ion therapy facilities have developed upright patient positioning prototypes, some of which were even coupled with upright CT[2]. Yet, upright RT has not achieved widespread application. Even in heavy ion therapy, the early upright positioning projects were discontinued in favor of heavy ion gantries despite their size and complexity. It is therefore important to not only highlight the potential advantages of upright RT, but to also discuss the challenges in transitioning from the established recumbent positioning to upright postures. Switching from recumbent to upright RT affects every step in the RT workflow. Anatomical differences between upright and recumbent are expected for nearly all target sites. Upright volumetric imaging therefore is paramount for simulation. It is yet unclear, however, whether CT, MRI and PET are all required in upright postures, or whether deformable image registration between recumbent and upright imaging, possibly enhanced by generative AI, can be sufficiently accurate to circumvent missing modalities in upright postures. In treatment planning, anatomical differences and the flexibility of upright positioning can provide a unique opportunity for optimization, but also come with a number of new parameters that need to be handled. While experience with upright RT is still limited and no guidelines for different target sites are established, this will mean an increased workload on medical physicists and clinicians. Uncertainties in patient setup, especially regarding anatomical differences and motion, need to be assessed with large patient cohorts to adjust margin recipes and robust optimization criteria for upright RT. While surface guidance imaging has proven in literature to be very useful for investigating external setup reproducibility in upright postures, it is not clear what level of internal imaging is needed at isocenter to ensure treatment accuracy. Immobilization equipment such as thermoplastic masks and vacuum cushions needs to be re evaluated for different upright postures and different body sites, due to the change in relative direction of gravity and becoming in part weight-bearing. This will be particularly challenging for pediatric patients, who might need anesthesia during the treatment. Not least, the overall facility design for upright RT needs to be defined. This involves careful evaluation of the feasibility of upright RT for different target sites. An option to switch to recumbent positioning for patients not eligible for upright may need to be considered. Both machine and patient-specific QA protocols have to be adjusted to the upright position. The design of upright positioning systems should take into account routine QA devices such as water-tank dosimetry. Finally, while the cost benefit seems clear for heavy ion therapy, for proton and photon therapy it is not straight-forward. The overall cost-effectiveness of upright RT depends on multiple factors such as workflow efficiency, the need for acquiring (possibly multiple) upright imaging solutions, as well as the cost of land at the facility location. In dense, urban areas, the reduced footprint of upright RT can present a relevant reduction in initial investment, but the same may not be true in rural regions or developing countries. Socio-economic impact analyses are required to support effective upright RT developments. Overall, upright RT presents a true paradigm shift compared to conventional recumbent positioning. It has the potential to transform RT to become more comfortable for patients, cheaper, and more effective. Still, there are many open questions and international guidelines for upright RT are lacking, which will be challenging for early adopters. However, this also provides a unique opportunity for innovation. Several centers having acquired upright RT solutions or already treating with upright postures, combined with the arsenal of advanced methods available to modern RT, including image guidance, AI, and motion mitigation strategies, leads to expect many ingenious solutions to the current challenges. Invited Speaker

References:

[1] Hegarty et al. (2022) Front. Oncol. 12:821887. doi:10.3389/fonc.2022.821887

[2] Volz et al. (2022) Front. Oncol. 12:930850. doi:10.3389/fonc.2022.930850