ESTRO 2023 - Abstract Book

S783

Monday 15 May 2023

ESTRO 2023

Conclusion DIBH reduced the NTCPs for RP for 92% and 2-year mortality for 74% of LA-NSCLC patients. While DIBH reduced the risk of RP consistently regardless of patient characteristics, the ability to reduce the risk of 2-year mortality was evident among patients with upper and left lower lobe tumors but not right lower lobe tumors. The anatomical changes that occur during DIBH, with compression and shifting of the heart and expansion of the lungs, have different effects on the risk of mortality depending on tumor location. OC-0936 Heartbeat simulation to evaluate intra-fraction dosimetric variations for 3 radiotherapy techniques N. Maffei 1 , B. Meduri 2 , F. Itta 3 , N. Ashraf 4 , M.V. Gutierrez 1 , A. Bernabei 1 , E. Zanella 5 , F. Di Pressa 5 , E. D'Angelo 5 , E. Mazzeo 5 , F. Lohr 5 , G. Guidi 1 1 Azienda Ospedaliero-Universitaria di Modena, Medical Physics, Modena, Italy; 2 Azienda ospedaliero-Universitaria di Modena, Radiotherapy Unit, Dept. of Oncology, Modena, Italy; 3 Azienda ospedaliero-Universitaria di Modena, Medical Physics, Modena, Italy; 4 University of Modena and Reggio Emilia, Physics, Modena, Italy; 5 Azienda Ospedaliero-Universitaria di Modena, Radiotherapy Unit, Dept. of Oncology, Modena, Italy Purpose or Objective A heartbeat cycle model was developed to simulate the cardiac motion during radiotherapy (RT) and to assess the intra fraction dosimetric effects on cardiac sub-structures comparing three planning techniques. Materials and Methods A Hierarchical-Clustering atlas-based algorithm were developed, validated and later used to automatically segment 25 cardiac sub-structures in 10 breast CTs acquired in Breath Hold technique. The heartbeat cycle was simulated starting from ventricles’ volume variations data from literature. A commercially deformable image registration algorithm was used to drive the motion model obtaining 2 synthetic CTs at the maximum and minimum heart expansion during the cardiac cycle. All the cardiac sub-structures were automatically contoured in deformed image sets. Intra-fraction dosimetric variations were evaluated for a left breast target (266cGy x 16fx) within 3 RT techniques: 3D Conformal Radiation Therapy (3D-CRT), Volumetric Modulated Arc Therapy (VMAT), Helical Tomotherapy (HT) for a total of 90 plans calculated. Dosimetric parameters evauated for each Regions of Interest (ROIs) were the average and the maximum dose. Automation of the workflow was performed by integrating developed IronPython scripts into the treatment planning system for auto contouring, creation of synthetic CTs and data extraction. Results The dosimetric analysis focused on ROIs closer to the high dose gradient in left breast target. 3D-CRT shows the lowest absolute Dose compared to the HT and VMAT but the wider range with the highest Dose values considering the total heart organ motion. In Left Ventricle (LV), VMAT shows the highest absolute dose compared to HT and 3D-CRT but relative doses are more robust. In Right Ventricle (RV), HT shows the highest absolute dose compared to VMAT and 3D-CRT with an improved target coverage and uniformity. In Proximal Left Anterior Descending Coronary Artery (ProxLADCA), Mid Left Anterior Descending Coronary Artery (MidLADCA) and Distal Left Anterior Descending Coronary Artery (DistLADCA), considering relative dose variations among cardiac cycle, 3D-CRT was the most affected by organ motion and VMAT was the most robust.