Comparison Between Breath-Hold and the Inspiratory Phase of Free Breathing in Left Breast Cancer Radiotherapy: Target Volume Coverage and Organ Sparing

Abstract

Background: Cardiac mortality and coronary events associated with left breast radiotherapy are correlated with the mean radiation dose to the heart. Methods: This prospective phase II study included left breast cancer patients receiving adjuvant locoregional radiotherapy with intensity-modulated radiation therapy (IMRT) following surgery. Patients were treated using the respiratory gating (RPM) technique (Varian Medical Systems, USA). Dosimetric outcomes were compared between deep inspiration breath-hold (DIBH) and the inspiratory phase of free breathing (FB) in the same patients, focusing on target volume coverage and sparing of critical organs (lungs, heart, and coronary arteries). The prescribed dose was 50 Gy in 25 fractions over five weeks to the chest wall or breast and/or lymph nodes, with an additional boost of 10 Gy in five fractions over one week to the tumor bed in breast-conserving surgery (BCS) cases. Two treatment plans were generated per patient: one for DIBH and another for the inspiratory phase of FB. Results: Between February 2020 and August 2022, 60 patients with a mean age of 50 years were enrolled in the study. The dosimetric analysis showed that the mean heart dose was lower in the DIBH group (4.8 Gy) compared to the FB group (6.4 Gy) with a statistically significant difference (p < 0.0001). Similarly, the mean dose to the left anterior descending artery (LAD) was significantly reduced in DIBH (14 Gy) compared to FB (20.5 Gy) (p < 0.0001). Regarding target volume coverage, the mean planning target volume (PTV) V95% was slightly higher in DIBH (97.3%) than in FB (96.5%) (p = 0.0062). The mean left lung V20 was comparable between the two techniques, with values of 14.4% in DIBH and 14.35% in FB (p = 0.85), indicating no significant difference in lung dose sparing. However, the mean left ventricular dose was significantly lower in DIBH (6 Gy) compared to FB (8.1 Gy) (p < 0.0001), further supporting the advantage of DIBH in reducing cardiac radiation exposure. Conclusion: DIBH plans demonstrated superior target coverage and significantly improved cardiac and coronary sparing compared to FB inspiratory phase plans. However, FB plans remained within acceptable dose constraints. No significant differences were observed in lung dose sparing or beam-on time.