Deep inspiration breath hold (DIBH) with electromagnetic surface transponder confirmation of chest wall (CW) position during radiation for left breast cancer.

Abstract

126 Background: DIBH during radiation of left breast cancers reduces heart dose, potentially reducing late cardiac ischemic events, but requires a treatment CW position significantly different from a free-breathing (FB) position. We sought to improve the accuracy of radiation therapy during DIBH by using electromagnetic surface transponders to track the position of the CW during treatment. We examined the benefit of this technique in reducing dose to the heart and consistently reproducing the DIBH position. We also evaluated the difference between FB and DIBH CW position and compared CW movement within the plateau of each DIBH to within beam-on time. Methods: 15 patients participated in this IRB-approved study. Patients were planned and treated using DIBH. We fused treatment-position FB CT scans to DIBH scans to compare mean heart (MH) and left anterior descending coronary artery (LAD) dose. We used surface transponder tracking reports to determine CW motion at the time of daily port films, during FB, the plateau of each DIBH, and beam-on time. We summed anterior and superior motion using the Pythagorean Theorem and report our results in this combined axis. Paired t-test was used to compare heart dose with vs. without DIBH and CW motion during plateau DIBH vs. beam-on. Results: DIBH significantly reduced MH and LAD dose vs. FB plans (MH 1.26 ± 0.51 Gy v 2.84 ± 1.55 Gy, p < 0.01), (LAD 5.49 ± 4.02 Gy v 18.15 ± 8.78 Gy, p < 0.01). DIBH CW position was a mean of 13.9 ± 5.3 mm anterior and superior to FB position. The mean difference in CW position at the time of daily port film vs. beam-on was -1.0 ± 2.5 mm. Plateau DIBH CW motion was 2.8 ± 2.3 mm, significantly increased from CW motion during beam-on (1.1 ± 1.2 mm, p < 0.01). Treatment was paused in 23% of fractions to adjust for suboptimal breath hold or CW position. Conclusions: DIBH reduced the MH and LAD dose by at least 50%. Real-time tracking with electromagnetic transponders allowed us to limit treatment to the most stable portion of the DIBH plateau, significantly reducing intra-fraction motion. Electromagnetic confirmation of CW position allowed verification of breath-hold reproducibility.