Normal tissue complication probability models of late cardiopulmonary toxicity following deep inspiration breath hold for breast cancer adjuvant radiotherapy.

BACKGROUND AND PURPOSE: Deep inspiration breath hold (DIBH) is a respiratory control technique designed to minimize cardiopulmonary toxicity induced by adjuvant radiotherapy for left-sided breast cancer. This study aimed to evaluate the dosimetric effects of DIBH compared with those of free breathing (FB) in patients undergoing postoperative radiotherapy for left-sided breast cancer in order to assess differences in potential cardiopulmonary complications between the two approaches. METHODS: Forty patients with left-sided breast cancer undergoing postoperative adjuvant radiotherapy were included. Of these, 20 patients received conventional radiotherapy (5000 cGy in 25 fractions), and the other 20 patients received hypofractionated radiotherapy (4005 cGy in 15 fractions, with a sequential boost to the tumor bed of 1000 cGy in 5 fractions). Treatment plans were performed on both FB and DIBH computed tomography images for each patient. Mean heart dose (MHD), mean left lung dose, and other cardiopulmonary parameters were recorded. The normal tissue complication probability (NTCP) model was applied to predict complications, including pericarditis/pericardial effusion, heart valvular dysfunction (RVD), coronary artery disease (CAD), and Radiation Therapy Oncology Group (RTOG) grade ≥ 2 radiation pneumonitis (RP). Clinical anatomical features, including the number of contact layers between the heart surface and the chest wall (defined as Contact_Heart) and the Haller index (HI), were also documented, followed by correlation analysis. RESULTS: The DIBH technique significantly reduced MHD by 22% in both conventional radiotherapy (P = 0.004, 95% confidence interval [CI][14, 31]) and hypofractionated radiotherapy (P = 0.003, 95% CI[14, 30]). DIBH also reduced the mean left lung dose by 10% in conventional radiotherapy (P = 0.010, 95% CI[2, 15]) and by 7% in hypofractionated radiotherapy (P = 0.008, 95% CI[0, 14]). Using the NTCP model to predict the risk of toxicities, DIBH reduced the predicted occurrence rates of pericarditis/pericardial effusion, RVD, CAD, and RTOG grade ≥ 2 RP by 35-39%, 46-51%, 4-7%, and 4-6%, respectively, across both treatment modalities. Contact_Heart was positively correlated with MHD but only weakly correlated with HI. CONCLUSION: DIBH significantly reduces radiation exposure to the heart and lungs in patients with left-sided breast cancer undergoing radiotherapy, potentially decreasing the risk of cardiopulmonary toxicity.