ESTRO 2024 - Abstract Book

S4150

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

assessment and simulate calculations in IMNIs of PMRT patient to enable real-time dose assessment of the heart and cardiac substructures during cardiac motion.

Material/Methods:

Fifteen patients with left breast PMRT were selected for this study, who were scanned with intravenous contrast using a GE Revolution APEX CT scanner (GE Healthcare, Waukesha, WI, USA) under voluntary breath-hold. A high-intensity deep learning image reconstruction algorithm (DLIR-H) was applied to reconstruct each patient's CCTA images at multiple stages of the cardiac cycle (0%-90%). According to the RTOG 1106 OAR atlas, including left ventricular (LV), right ventricular (RV), right atrial (RA), left atrial (LA), right coronary artery (RCA), and left anterior descending artery (LAD) contouring were conducted. For these contours, rigid registrations were performed at each phase and TPCT to replicate these cardiac substructures on TPCT images. To assure the accuracy of the CT electron density, we redefined the replicated cardiac structures to have a CT value of 0 and the redundant cardiac structures on the TPCT to have a CT value of -1000. To ensure consistency, the target volume and the organs at risk were defined by one physician, and the target volume for all enrolled patients included the IMNs, with the addition of a 0.5-cm virtual bolus in each set of images. We used Elipse 15.6 (Varian Medical Systems, Palo Alto) to design the VMAT plan in TPCT additionally used the AXB algorithm to perform the calculations, and then copied the irradiation fields to each phase and performed the calculations. After the calculations, the dosimetric parameters to heart substructures of the 10 phases were accumulated and compared to the routine plan.

Results:

The absolute difference in average heart Dmean between the accumulated plan and the conventional plan was 71.2 cGy, ranging from 211.8 cGy to 17.7 cGy. The proportion of average heart Dmean of the dosimetric differences to the accumulated dose to heart was 12%. Of the six contouring substructures, comparing the two plans, the Dmean of LAD and RAD had larger absolute differences of 387.5cGy and 195.8cGy, respectively. Followed by LV and RA with an average Dmean of 117.7cGy and 93.3cGy. The ratio of the dose to their average difference for each patient's cardiac substructure was 22.5% for LAD and 34.7% for RAD. This was succeeded by RA and RV, which also had a ratio of 18.1% and 17.1% of their Dmean, respectively.