ESTRO 2025 - Abstract Book

S23

Invited Speaker

ESTRO 2025

and developing new QA protocols) to dose delivery and patient follow-up, requiring comprehensive re-tooling of processes and staff training. Encouragingly, many research initiatives are underway to tackle these challenges and build the evidence base, accelerating the clinical integration of upright proton therapy. Looking ahead, the impact of adopting upright proton therapy could be profound. By vastly reducing costs, complexity and physical footprint, this technology can make proton and heavy-ion treatments far more available globally, potentially fitting high-end particle therapy capabilities into single-room facilities and resource-limited settings. The improved efficiency and flexibility of a gantry-less, patient-rotating system also enhance the sustainability of proton therapy centres, helping avoid the financial pitfalls that have plagued some large proton installations. Ultimately, upright proton therapy offers a pathway to democratize advanced radiotherapy by enabling more centres to deliver cutting-edge techniques like proton arcs, FLASH-RT, and real-time MR guided adaptive treatments, thereby improving patient access and treatment outcomes worldwide in the coming years.

4681

Speaker Abstracts Online-adaptive PT Stefan Both Radiation Therapy, University Medical Center Groningen, Groningen, Netherlands

Abstract:

Adaptive Proton Therapy (APT) represents a significant advancement in precision cancer treatment, enabling real time or near-real-time modification of proton therapy plans between or during treatment sessions. APT ensures precise targeting of tumors while effectively sparing surrounding healthy tissues, even with reduced robustness margins. It accounts for variations such as tumor shrinkage, patient weight changes, organ movement, and biological alterations detected through advanced imaging modalities like MRI and PET. Throughout a typical radiotherapy course, spanning several weeks, patients may experience anatomical changes that can significantly impact treatment accuracy and efficacy. Examples include weight fluctuations affecting tissue density, tumor shrinkage or reshaping, and internal organ repositioning. These interfractional and intrafractional changes may lead to deviations from planned dose distributions, potentially compromising tumor control or increasing toxicity to healthy tissues. APT addresses these issues by allowing clinicians to continuously refine treatment plans based on up-to-date anatomical, dosimetric, and biological imaging data, enabling dose optimization—such as increasing tumor dose, reducing exposure to organs at risk, shrinking target volumes for responsive tumors, and escalating doses selectively to target sub-volumes. Triggers for implementing APT include clear indicators of anatomical, dosimetric, and clinical-biological changes detected during the treatment course. Recognizing these indicators promptly allows timely adaptations to maintain optimal treatment effectiveness. The full clinical realization of efficient APT necessitates significant technological advancements to manage the increased workload online, minimizing reliance on extensive manual resources. Several key challenges must be addressed to effectively integrate APT into clinical settings.High-quality frequent imaging is necessary to monitor anatomical and biological changes accurately. Incorporating adaptive planning into clinical workflows requires efficient processes to minimize delays, including rapid imaging, autocontouring, plan adaptation, and quality assurance. Advanced treatment planning systems capable of near real time recalculations and seamless integration with imaging modalities are essential. Implementing adaptive workflows demands additional time and expertise from clinical staff, necessitating appropriate training and resource management. Artificial Intelligence in conjunction