S2845
RTT - RTT education, training, and advanced practice
ESTRO 2026
correlations and limited-to-full heart volume ratios assessed consistency and robustness across truncation levels. Results: All limited-heart surrogate metrics showed strong and statistically significant correlations with MHD (p < 1e- 4). D20cc_lim and D40cc_lim demonstrated strong correlations (r 0.81–0.85, ρ 0.85–0.88; R ² 0.65–0.72, RMSE 0.69–0.77Gy). 100cc_lim remained moderate to strong (r 0.77, ρ 0.75; R ² 0.59; RMSE 0.83 Gy). MHD_lim showed the strongest correlation (r 0.956, ρ 0.948; R ² 0.914, RMSE 0.381 Gy), particularly within the 1–3 Gy range, where linearity was maintained with minimal residuals (Figure 2). Limited heart volumes ranged from 15.5%–94.3% of the full-heart volume (51.7 ± 20.6%), yet MHD_lim remained highly predictive. Importantly, strong correlations were maintained across both DIBH and FB cohorts.
Proffered Paper 554 Integrating Mean Heart Dose Surrogates into an AI-Compatible Workflow for Daily Cardiac Monitoring in Breast Radiotherapy Rhoda Broni 1 , Aodh MacGairbhith 1 , Caitriona Kelly 1 , Jill Nicholson 1,2 , Frances Duane 1,2 , Ciaran Malone 1,3 1 St. Luke’s Radiation Oncology Network, St. Luke’s Hospital, Dublin, Ireland. 2 Trinity St. James’s Cancer Institute, Trinity College Dublin, Dublin, Ireland. 3 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, Netherlands Purpose/Objective: Estimating mean heart dose (MHD) during breast radiotherapy is challenging when cone-beam CT (CBCT) field-of-view (FOV) only partially visualizes the heart, a limitation that persists even with AI-based synthetic imaging for monitoring and adaptation (Figure 1). This study aimed to identify robust, dosimetric surrogates for accurately estimating MHD from truncated cardiac structures. The overall goal was to determine a metric that best predicts MHD for CBCT-to-synthetic CT (sCT) frameworks, enabling workflow-friendly, vendor neutral, RTT-led daily heart- dose monitoring and adaptive decision-making, even with incomplete cardiac imaging.
Conclusion: These findings introduce the first robust dosimetric surrogate metrics for daily heart dose monitoring under limited CBCT FOV conditions, maintaining predictive accuracy even when only 15.5–94.3% of the heart is imaged. The range of heart truncation ensures results are applicable to the FOV capabilities of a wide range of old and new CBCT imaging systems. MHD_lim, in particular, could be integrated into AI- assisted adaptive workflows including synthetic CT frameworks to enable RTT-led decision-making and long-term cardiac risk reduction in breast radiotherapy. Keywords: CBCT, adaptive RT, RTT-led
Material/Methods: 59 patients (48 deep inspiration breath-hold (DIBH), 11 free-breathing (FB)) receiving 40 Gy in 15 fractions were retrospectively analysed to represent a broad range of cardiac positions and dose levels of clinical variability. Full-heart structures were contoured on planning CTs, while limited-heart structures were created by constraining the full-heart contours to the CBCT FOV, simulating truncation during treatment. Heart structures were shifted 3, 5 and 7 mm toward the treatment fields to simulate typical treatment variability, resulting in 205 structures (original + shifted). Practical dose-volume surrogates (D20cc_lim, D40cc_lim, D100cc_lim) and limited mean heart dose (MHD_lim) were derived and compared with true MHD from planning CTs. Pearson (r) and Spearman ( ρ )
Digital Poster 667
Does the use of Surface-Guided Radiotherapy during Stereotactic Radiosurgery improve the accuracy of patient setup?
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