63 Myocardial fibrosis in esophageal cancer patients Extraction of dose-volume parameters For evaluation of radiation dose distributions, the original planning CT scans and corresponding treatment plans and delineated structures of each patient were transferred to the Mirada Medical treatment planning system (version 1.2.0). Additional contouring of the different substructures of the heart; the left ventricle (LV), right ventricle (RV), left atrium (LA) and right atrium (RA), were automatically contoured in Mirada using an atlas-based tool. All structures were checked and adapted according to the cardiac contouring atlas of Feng et al.[21] In addition, the myocardium of the left ventricle was defined and divided in 17 segments corresponding with the standardized myocardial 17-segment model in order to find relations in dose distributions and cardiac MRI measures.[22,23] The workflow to create these segments is shown in figure 1. Figure 1. Workflow for segmentation of the 17 myocardial segments of the left ventricle on radiation therapy planning computed tomography (CT; according to the 17-segment model proposed by the American Heart Association) 1. Angulate planning CT perpendicular to the long axis of the left ventricle to create a short axis view; 2. Check and adjust contours of whole heart (WH), left ventricle (LV), right ventricle (RV), left atrium (LA), and right atrium (RA); 3. Create left ventricular wall (1 cm thick); 4. Define basal, mid, and apical slices (devide ventricle where lumen is visible into 3 equal slices) and segment 17 (true apex); 5. Divide the basal and mid part in 6 equal segments (60? angle). Divide the apical part in 4 equal segments (90? angle). Start with the septal segments (2, 3, 8, 9, and 14) for adequate positioning; 6. Angulate CT with new structures back to normal position. 7. Extract dose-volume histogram parameters for WH, LV, RV, LA, RA and segment 1 to 17. On the left side, an example is showed of an angulated planning CT (short axis view) and the method of delineation of the heart substructures and myocardial segments on a midventricular slice. The right picture demonstrates the ability to obtain dose parameters per (sub)structure using this 3-dimensional model of the heart. 5
RkJQdWJsaXNoZXIy MTk4NDMw