Heart-Sparing Capability and Positional Reproducibility of Continuous Positive Airway Pressure in Left-Sided Breast Radiation Therapy

Abstract

Purpose: Our purpose was to investigate the interfraction and intrafraction reproducibility and practical applicability of continuous positive airway pressure (CPAP) for left breast volumetric modulated arc therapy (VMAT). Methods and Materials: Interfraction reproducibility of the position of the heart was evaluated by measuring the heart-to-target distance on 20 planning computed tomography (CT) and 300 daily cone beam CT of 20 patients with left breast cancer treated with a 15-fraction VMAT. The dosimetric metrics of the whole heart and its substructures were compared between CPAP and free-breathing based VMAT plans. Intrafraction reproducibility was evaluated by measuring the motions of the breast target and diaphragm in 4-dimensional CT of 20 female patients with nonbreast cancer. Lastly, we analyzed the CPAP compliance data of 237 consecutive patients with left-sided breast cancer with and without internal mammary node irradiation (IMNI). Results: The heart position was reproducible as evidenced by an absolute average heart-to-target distance error of 2.0 ± 2.0 mm. Compared with free-breathing, CPAP significantly reduced the mean heart dose and the dose to the left ventricle and left anterior descending artery. The average intrafraction position variation of the breast target was 0.5 ± 0.5, 2.5 ± 2.0, and 1.8 ± 1.4 mm in the mediolateral, craniocaudal, and anteroposterior directions, respectively. CPAP was successfully applied in 221 patients (93%), with a mean heart dose of 1.6 ± 0.7 Gy (IMNI: 2.0 Gy and no IMNI: 1.1 Gy). Conclusions: CPAP has adequate heart-sparing capability and sufficient reproducibility in VMAT for left-sided breast cancer treatment, with a high compliance rate. Thus, CPAP is applicable in routine practice for left-sided breast cancer radiation therapy.