Continuous positive airway pressure in breast cancer radiotherapy: Protocol of a prospective clinical trial.

Background: Radiotherapy (RT) improves survival and local control after breast-conserving surgery (BCS) for breast cancer (BC) but can also cause toxicity. Preliminary studies suggest that continuous positive airway pressure (CPAP) reduces organ-at-risk (OAR) doses in left-sided BC RT. This prospective trial evaluates whether CPAP reduces OAR doses in a larger patient cohort, including both left and right-sided cases, and identifies which patients benefit most. Furthermore, this study investigates the feasibility of CPAP in BC RT, by evaluating patient comfort, radiation time, accuracy and reproducibility. Methods: BC patients requiring BCS and RT are prospectively enrolled -left-sided cases with or without regional nodal irradiation (RNI), or right-sided cases requiring RNI. Each patient undergoes an additional CT simulation with CPAP-free breathing (FB) for right-sided cases and deep inspiration breath hold (DIBH) for left-sided cases. Left-sided patients unable to perform DIBH or ≥ 70 years old are evaluated in FB. Two RT plans (with and without CPAP) are compared. If CPAP reduces mean heart or contralateral breast dose by ≥0.5 Gy, or mean lung dose by ≥1 Gy, treatment is delivered with CPAP. Patient comfort is assessed through surveys. Sample size calculations indicated that 53 patients are required to detect a ≥0.5 Gy reduction in mean heart dose. Discussion: This is the first large, prospective study to evaluate CPAP in both left- and right-sided BC patients, aiming to demonstrate OAR dose reductions and assess feasibility. The final aim is to provide patient-selection models and guidelines for clinical implementation. Trial registration: The study is registered on Clinicaltrials.gov (NCT07373782).