1232 - A Novel Split-Field and Switching Breath-Hold Strategy for Maximal Heart Sparing in Left-Sided Postmastectomy Radiotherapy

08:20am - 08:25am ET

Room 107

Presenter(s)

Wenxiang Li, PhD, MS - The First affiliated Hospital Zhejiang University School of Medicine, Hangzhou, Zhejiang

W. Li, L. Bu, L. Wu, Z. Sun, Y. Yan, L. Wang, Z. Lu, F. Zhao, and S. Yan; Department of Radiation Oncology, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China

Purpose/Objective(s):

Deep inspiration breath-hold (DIBH) achieves excellent cardiac sparing in left breast radiotherapy, and our previous work demonstrated that abdominal DIBH (A-DIBH) further enhances this protection while maintaining stable target reproducibility. To maximize sparing efficacy, particularly for high-risk cardiac substructures, we investigated a novel Split-Field Switching Breath-Hold (SF-SBH) strategy. We hypothesized that dynamically switching respiratory phases between split fields minimizes the tangential heart volume. This study quantifies dosimetric reductions to the heart and substructures versus A-DIBH, and identifies objective predictors for optimal patient selection.

Materials/Methods:

Fifty-six left-sided post-mastectomy breast cancer patients were trained in A-DIBH and abdominal end-expiration breath-hold (A-EEBH). To determine the optimal SF-SBH switching plane, we evaluated every axial plan target volume (PTV) slice. For each candidate slice, we summed the tangential heart volume of the cranial portion (using A-DIBH) and the caudal portion (using A-EEBH). The slice yielding the minimum combined volume was selected. VMAT plans (50 Gy/25 fractions) split fields at this plane. Deformable dose accumulation extracted mean doses and V5-V40 for the heart, LAD, high-risk cardiac zone (HRCZ: 1 cm-thick wall centered on LAD with 3.5 cm lateral margins), and ventricles. Target deviations and coverage were assessed via rigid registration. Spearman correlation evaluated objective predictors of dosimetric benefit.

Results:

SF-SBH significantly reduced mean doses (cGy) across all cardiac structures vs. A-DIBH: heart (384±91 vs. 270±76), LAD (1279±685 vs. 817±430), HRCZ (1072±464 vs. 760±344), left ventricle (383±130 vs. 278±114), and right ventricle (408±144 vs. 304±115) (all p < 0.001). Substructure V5-V40 parameters also decreased significantly (p < 0.005). Rigid registration errors during the SF-SBH transition were minimal (median LR/AP/SI: 1.1/2.1/1.7 mm). PTV coverage was comparable between SF-SBH and A-DIBH (94.3±1.2% vs. 95.2±0.8%, p = 0.47). Regarding objective predictors, dosimetric benefit correlated strongly with baseline A-DIBH mean heart dose (MHD) and tangential heart volume reduction (?V_tan). Specifically, ?MHD correlated with baseline MHD (? = 0.69) and ?V_tan (? = 0.62), while HRCZ dose reduction (?M_HRCZ) correlated similarly (? = 0.78 and 0.75).

Conclusion:

The novel SF-SBH strategy overcomes anatomical dosimetric bottlenecks in left-sided post-mastectomy radiotherapy. By dynamically switching respiratory phases, it minimizes tangential heart volume, significantly sparing the heart and high-risk substructures (LAD, HRCZ) while maintaining robust target coverage. Patients with higher baseline A-DIBH cardiac doses derive the greatest benefit. Baseline MHD and ?V_tan serve as reliable objective predictors for patient selection, establishing SF-SBH as a feasible paradigm for advanced cardiac sparing.