Deep inspiration breath-hold technique for left-sided breast cancer: An analysis of predictors for organ-at-risk sparing

To identify anatomic and treatment characteristics that correlate with organ-at-risk (OAR) sparing with deep inspiration breath-hold (DIBH) technique to guide patient selection for this technique. Anatomic and treatment characteristics and radiation doses to OARs were compared between free-breathing and DIBH plans. Linear regression analysis was used to identify factors independently predicting for cardiac sparing. We identified 64 patients: 44 with intact breast and 20 postmastectomy. For changes measured directly on treatment planning scans, DIBH plans decreased heart-chest wall length (6.5 vs 5.0cm, p < 0.001), and increased lung volume (1074.4 vs 1881.3cm³, p < 0.001), and for changes measured after fields are set, they decreased maximum heart depth (1.1 vs 0.3cm, p < 0.001) and heart volume in field (HVIF) (9.1 vs 0.9cm³, p < 0.001). DIBH reduced the mean heart dose (3.4 vs 1.8Gy, p < 0.001) and lung V₂₀ (19.6% vs 15.3%, p < 0.001). Regression analysis found that only change in HVIF independently predicted for cardiac sparing. We identified patients in the bottom quartile of the dosimetric benefits seen with DIBH and categorized the cause of this "minimal benefit." Overall, 29% of patients satisfied these criteria for minimal benefit with DIBH and the most common cause was favorable baseline anatomy. Only the reduction in HVIF predicted for reductions in mean heart dose; no specific anatomic surrogate for the dosimetric benefits of DIBH technique could be identified. Most patients have significant dosimetric benefit with DIBH, and this technique should be planned and evaluated for all patients receiving left-sided breast/chest wall radiation.