S2933
RTT- RTT operational practice and workflow innovations
ESTRO 2026
Oncology, GenesisCare, Sydney, Australia. 5 ImageX Institute, University of Sydney, Sydney, Australia
Purpose/Objective: In breast radiotherapy (RT), daily anatomical
variations, particularly involving the radiosensitive heart1 and chest wall can occur even when patient setup appears within tolerance on surface guidance or respiratrory guided verification. Current clinical workflows lack efficient tools to routinely quantify the resulting dosimetric impact, leaving uncertainty as to whether such variations have a clinically relevant effect on delivered dose. The aim of this study was to evaluate the impact of an automated software solution that integrates daily cone beam CT (CBCT) images to calculate delivered dose distributions that quantifies dosimetric deviations arising from inter- fraction anatomical changes during breast RT. Material/Methods: Five patients (at least 15 fractions each) who received deep inspiration breath-hold (DIBH) breast RT with surface-guided or respiratory assisted positioning were included from an ethics-approved retrospective patient dataset (2024-09-1157). For each fraction, cone beam CT (CBCT) images were automatically processed by the software. For each CBCT, deformable registration was performed by the software without human intervention, resulting in a synthetic CT, on which the treatment delivered dose was calculated. Heart and clinical target volume (CTV) daily calculated dose were compared to planned values. Results:
Conclusion: Implementing MRI-in-treatment-position for HPB radiotherapy required extensive sequence optimisation, documentation, and staged multidisciplinary coordination. Diagnostic radiographers and RTTs played complementary roles in developing and delivering the workflow, demonstrating that shared professional oversight can enable safe, efficient, and clinically relevant imaging integration. Although resource-intensive, the process proved achievable through structured planning, protected time, and institutional support. This staged approach addresses a key evidence gap in MRI workflow development and provides a scalable model for advanced imaging adoption within value-based radiotherapy practice. Keywords: MRI, motion management, implementation Quantifying the Dosimetric Impact of Daily Anatomical Variations in Breast Radiotherapy Using Automated Cone Beam CT (CBCT) Based Dose Reconstruction Shivani Kumar 1 , Adam Mylonas 2 , Brendan Whelan 2 , Sean Pollock 3 , Michael Jameson 4 , Doan Trang Nguyen 1 , Paul Keall 1,5 1 Clinical Research, SeeTreat, Sydney, Australia. 2 Engineering, SeeTreat, Sydney, Australia. 3 Product Development, SeeTreat, Sydney, Australia. 4 Radiation Mini-Oral 3172
The automated workflow successfully processed 75 fractions. Despite breath-hold verification within tolerance during treatment delivery, dosimetric variations was found to have occurred in a subset of fractions. Heart D0.03cc exceeded 2% deviation in 69% of fractions and 5% deviation in 48% of fractions(Fig2). Maximum heart D0.03cc deviation was 39% above planned values. Mean heart dose varied by -4.7% (range: -53.2% to +38.9%). Target coverage (CTV D95%) showed >2% deviation in 37% of fractions and >5% deviation in 20% of fractions (Fig2). In one patient,
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