2686 - The Value of Deep Inspiratory Breath Hold (DIBH) in Right Sided Breast Cancer Radiotherapy

Purpose/Objective(s): Deep inspiration breath hold (DIBH) is well established for reducing cardiac dose in left-sided breast radiotherapy, but its role in right-sided treatment is less clear. Using an intra-patient dosimetric comparison, we aimed to evaluate the benefits of DIBH compared to free-breathing (FB) when treating patients with right-sided breast cancer. We hypothesized that DIBH reduces right lung and heart dose compared with FB, particularly in plans requiring regional nodal irradiation (RNI), while maintaining equivalent target coverage.

Materials/Methods: Consecutive patients who received left-sided breast irradiation in 2023 were identified, for whom both FB and DIBH computed tomography (CT) simulation scans were available. For each patient, organs at risk were contoured, and six plans were generated using three dimensional-conformal radiation therapy, three on the FB scan and three on the DIBH scan, to enable intra-patient dosimetric comparison. The plans included: (1) right-sided whole-breast tangents (TG), (2) right-sided whole-breast tangents plus supraclavicular (TG + SCV) field, and (3) right-sided whole breast and internal mammary chain (IMC) wide tangents (WT) with SCV coverage. Dosimetric parameters for the right lung, heart, and right coronary artery (RCA) were extracted. Paired two-tailed t-tests were used for all intra-patient comparisons (p < 0.05 considered significant).

Results: A total of 120 treatment plans from 15 consecutive patients were generated. For breast-only tangents, DIBH reduced right lung V20 from 16.1% to 12.4% (p < 0.001), although mean right lung dose was not significantly different (8.11 vs 7.59 Gy, p = 0.396). For tangents plus SCV plans, DIBH significantly decreased right lung V20 from 25.0% to 16.3% (p < 0.001) and mean lung dose from 12.6 to 8.94 Gy (p < 0.001). Heart (0.78 vs 0.73 Gy, p = 0.327) and RCA (1.36 vs 1.11 Gy, p = 0.055) doses were not significantly changed. The largest benefit occurred with WT plus SCV plans, where DIBH reduced right lung V20 from 35.0% to 24.8% (p < 0.001) and mean lung dose from 17.9 to 12.5 Gy (p < 0.001). Mean heart and RCA doses were minimally affected (heart 1.04 vs 0.97 Gy, p = 0.077; RCA 2.22 vs 1.59 Gy, p = 0.060). Target coverage was maintained across all plans.

Conclusion: DIBH in right-sided breast radiotherapy significantly reduces right lung dose, particularly for patients requiring RNI with WT. By reducing ipsilateral lung V20 and mean dose, DIBH has the potential to lower the risk of radiation pneumonitis. These results support the selective use of DIBH for right-sided breast cancer patients, especially in RNI settings.