ESTRO 2022 - Abstract Book

S758

Abstract book

ESTRO 2022

during irradiation. This talk will discuss the pros and cons of several real-time radiotherapy adaptation techniques such as tracking, trailing, gating and intra-fractional replanning. Practical examples will emphasize MRI-guided radiotherapy. The discussion will differentiate between the real-time requirements for respiratory adaptation and cardiac adaptation. Increasingly, treatment targets within or near the heart are considered for radioablation. Cardiac frequencies are typically four times higher compared to breathing frequencies and thus present a unique challenge for real-time imaging and treatment adaptation techniques.

SP-0859 Slow intrafraction motion: MRI-based handling of non-periodic target deformations

P. Bonomo

Italy Abstract not available

SP-0860 Real-time dose-guided treatment adaptation

S. Skouboe 1

1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark

Abstract Text Anatomical changes may greatly impact the delivered radiotherapy dose in a negative way like tumor underdosage or organs at risk overdosage. Treatment plans can be adapted to the anatomy of the day right before starting the treatment, either by shifting the couch by matching anatomies from CBCT with planning CT, or by deformable image registration or re- contouring and re-optimizing the treatment plan. However, this cannot account for in-treatment anatomical changes, such as respiratory-induced motion. This issue has been tackled by various clinical trials on real-time adaptations such as using gating (switching the treatment beam on and off depending on target location), MLC-tracking (moving the treatment beam to where the target is) or couch-tracking (moving the patient in the opposite direction of internal motion to keep the target in place). However, these solutions are geometric and instantaneous in nature, thus unable to solve suboptimally delivered dose earlier in the treatment fraction. A more clinically relevant metric than tumor position for plan adaptation is the delivered dose. In this presentation, I will give a brief overview of the literature on calculating the dose in real-time taking time-resolved anatomical changes into account, and ideas on how to act in real-time based on the dose. This will cover calculating the dose with simplistic approaches, EPID-based solutions and Monte Carlo solutions, taking real-time anatomical changes into account. The ideas for adaptation will cover dose-guided gating, MLC and couch tracking, couch corrections (by estimated final dose for numerous couch-shift scenarios) and plan re-optimizing on-the-fly, all with and without dose-repair functionalities.

SP-0861 Adapting to biological response based on quantitative imaging, peripheral blood, and tissue markers: Next- generation personalized radiation oncology

S. Bowen 1

1 University of Washington, Radiation Oncology, Radiology (joint), Seattle, USA

Abstract Text Despite the growing arsenal of therapeutics for patients with advanced cancer, not all patients benefit from population- based treatment regimens. Quantitative imaging as a biomarker of biological response can be leveraged both for patient risk stratification and for spatially guided treatment adaptation / intensification. Peripheral blood biomarkers of the immune response and systemic disease burden can complement localized biological imaging assessments and tissue molecular diagnostics. This talk will present an overview of biological response-adaptive radiation therapy in clinical trials, comparing and contrasting different approaches. Ongoing investigations on the clinical utility of quantitative imaging and peripheral blood biomarkers as complements to tissue markers will be summarized in the context of emerging paradigms that seek to personalize radiation and immune modulating systemic therapy combinations.

Debate: This house believes that brachytherapy is a dying art

SP-0863 For the motion

S. Perryck

Switzerland Abstract not available

SP-0864 Against the motion