Room: AAPM ePoster Library
The respiratory cycle is dynamic and anisotropic. Since DIBH breast treatment typically uses an ROI much larger than the actual target, it may underestimate the true underlying breathing amplitude. We propose an evidence-based ROI that takes breathing anisotropy and variation into account. This ROI can enhance tracking sensitivity and detect breast motion to the millimeter.
A phantom was immobilized on a Linac couch. A reference surface image was captured by a 3D surface imaging system and a large ROI was created. To simulate local breast motion, several circular plates of different diameters(d) and heights(h) were placed on the phantom right chest and corresponding translational shifts were measured. Additionally, a circular clay [15.3(d)x0.3(h)cm] was placed conformally on the phantom chest to determine the maximum ROI that could detect a 3-mm amplitude change. We also retrospectively analyzed the CT scans of 7 breast DIBH patients and measured breathing amplitude changes in the breast and surrounding anatomy relative to their corresponding free breathing (FB) CT scans.
For the 12.8(d)x3.8(h)cm plate, the measured translational shifts were VRT=0.00, LNG=0.00, and LAT=0.00 cm. For the 15.3(d)x4.0(h)cm plate, the measured shifts were VRT=0.56, LNG=-0.49, and LAT=0.16 cm. For the 22.0(d)x2.0(h)cm plate, the measured shifts were VRT=1.00, LNG=0.68, and LAT=0.47 cm. To reach a tracking sensitivity of 3mm, the ROI had to be approximately the same size as the moving target. The mean breast amplitude change caused by DIBH was at least 0.5 cm greater than its surrounding anatomy by FB.
The ROI should be patient-specific and general population-based approaches should be avoided. Breathing amplitude changes between DIBH and FB in the breast and surrounding anatomy should be evaluated. Given an action threshold of 3 mm, the ROI should exclude surface areas that have a breathing amplitude change >3 mm for DIBH breast tracking.
Funding Support, Disclosures, and Conflict of Interest: This research was funded in part through the NIH/NCI Cancer Center Support Grant P30 CA008748