ESTRO 2024 - Abstract Book

S680

Clinical - Breast

ESTRO 2024

In the personalized approach, patients were instructed to practice 1) natural-DIBH first, 2) if good compliance of natural-DIBH observed, they were asked to do belly-DIBH, and 3) if good compliance of belly-DIBH observed, they were asked to use both belly and chest, starting with belly and then chest to achieve ultimate-DIBH. Once practice done, CT scans were made in the order of free breathing (FB) scan, ultimate-DIBH scan and natural-DIBH scan. Note any non-compliant DIBH scan was skipped. No trainer-dependent variation existed since every simulation was carried out by single physicist. 26 consecutive patients with either left- or right-sided breast cancer underwent RT to the whole breast or chest wall and regional nodes following mastectomy or breast-conserving surgery were retrospectively analyzed. After simulation CT images were acquired, the physician contoured the target and necessary structures. To evaluate the clinical benefit of the ultimate-DIBH, in terms of heart and lung dose exposure, we calculated the maximum heart distance (MHD), which is the distance of heart within treatment fields in the three set of images and compared the MHD between FB and natural-DIBH, between FB and ultimate-DIBH and between ultimate-DIBH and natural-DIBH. The MHD was calculated as the maximum distance between the heart contour and the posterior edge of the tangent as measured on the medial or lateral beams-eye-view images. MHD has been shown to be correlated well with mean heart dose. In addition, the left and right lung volumes were also compared between FB and DIBH and between the DIBH techniques. Wilcoxon signed rank tests were performed to test the statistical significance of differences in MHD and lung volumes between FB and DIBH and between the two DIBH techniques.

Results:

All of the 26 patients were able to comply with one of the DIBH techniques. Within them, 19 (73%) and 7 (27%) patients were treated with the ultimate-DIBH technique and the natural-DIBH, respectively, based on their compliance and quick image evaluation during simulation. Among 7 patients who were treated with natural-DIBH, 4 (15%) patients were unable to comply with ultimate-DIBH, 2 (8%) patients had better heart separation with natural DIBH and 1 (4%) patient had no significant difference. The MHD and left lung volume by the three breathing modes for the 11 left breast patients with complete datasets are shown as bar plots in figure 1. The right lung volume for the 5 right breast patients with at least two datasets are also shown. The ultimate-DIBH has the smallest MHD (7mm) and the largest left and right lung volumes (2111 cm3 and 2617 cm3, respectively). The mean difference of