KEY POINTS
- The paper grew from the 2024 ESTRO physics workshop on gantry-less radiotherapy, where 22 participants from clinical physics, radiation oncology, academia and industry reviewed current evidence, implementation barriers and priorities for clinical translation.
- Instead of rotating a heavy treatment gantry, upright systems use a fixed beam while rotating the seated or standing patient. The concept could substantially reduce room footprint, installation complexity and cost, particularly for particle therapy, while preserving access to multiple beam directions.
- Early evidence spans head and neck, breast, thoracic, abdominal and pelvic applications, but remains dominated by small feasibility cohorts. One published upright proton series included 51 chordoma/chondrosarcoma patients, while a 10-patient head-and-neck experience reported residual positioning errors of roughly 1–2 mm in individual axes.
- Imaging is one of the major unresolved bottlenecks. Upright CT systems exist, but MRI and PET will often remain supine, creating a need for validated deformable registration or synthetic imaging and explicit management of posture-dependent anatomical changes.
- Immobilization and chair mechanics must be treated as components of the treatment-delivery system rather than simple accessories. End-to-end QA must verify coordinate transformation between imaging, chair rotation and beam delivery, while patient-specific QA may require vertically mounted or nozzle-mounted measurement systems.
- Non-coplanar treatment remains particularly challenging because changing chair tilt changes internal anatomy under gravity; in some scenarios, separate imaging could be required for different treatment orientations.
- Because clinical evidence remains sparse, the authors identify palliative RT as a logical early clinical use case, allowing centres to establish positioning, imaging and workflow reliability before expanding into more complex curative treatments.
CLINICAL TAKEAWAY
Upright RT is moving from an engineering concept toward a clinically implementable treatment platform, with potentially major implications for proton-therapy cost and accessibility. The limiting factor is no longer simply whether a chair can rotate accurately: robust upright imaging, motion management, QA and prospective clinical evidence are now the key requirements before broad adoption.