2776 - PROTECT-CPAP: A Prospective Study of Cardiac and Pulmonary Dose Reduction Using Continuous Positive Airway Pressure in Left-Sided Breast Radiotherapy

Purpose/Objective(s):

Radiation-induced cardiac toxicity remains a major concern in left-sided breast cancer radiotherapy. While deep inspiration breath hold (DIBH) reduces cardiac dose, its use is limited by patient compliance, prolonged treatment time, and infrastructure requirements. Continuous positive airway pressure (CPAP), through passive lung hyperinflation and cardiac displacement, may provide comparable cardiac sparing with improved workflow efficiency. This prospective study evaluates the dosimetric, geometric, feasibility, workflow, and patient-reported outcomes of CPAP as an alternative cardiac-sparing strategy.

Materials/Methods:

Seventeen patients with left-sided breast cancer underwent paired CT simulation in free breathing (FB) and under CPAP (15 cm H2O) in this prospective interim dosimetric analysis (May 2025–April 2026). Identical IMRT plans were generated on both datasets. Primary endpoints were mean heart dose and LAD mean dose. Secondary endpoints included heart V17, LAD Dmax, lung dosimetry, geometric parameters, and machine occupancy. Patient-reported outcomes were assessed using EORTC QLQ-C30 and an investigator-developed CPAP comfort questionnaire. Workflow feasibility was documented using structured session forms. Machine occupancy was compared with a matched ABC-DIBH cohort (n=17). Shapiro-Wilk normality testing guided use of paired t-test or Wilcoxon signed-rank tests; Kruskal–Wallis test compared sparing across treatment complexities (local, regional, regional+IMC). All tests two-sided (p<0.05); analyses performed in R (v4.3.1).

Results:

CPAP significantly increased left and right lung volumes by 336 cc (41%) and 361 cc (36%), respectively (p<0.001), increased SSN–heart distance by 1.31 cm (p<0.001), and reduced heart volume by 39.5 cc (p=0.015). Mean heart dose decreased by 48% (6.54 to 3.40 Gy), heart V17 by 53% (9.57% to 4.52%), LAD mean dose by 61% (17.22 to 6.75 Gy), and LAD Dmax by 40% (27.51 to 16.49 Gy) (all p<0.001). Cardiac sparing was consistent across all treatment complexities (p=0.4). Ipsilateral lung V17 remained stable (FB: 22.89±2.25% vs. CPAP: 23.01±2.10%, p=NS), with mean lung dose <10 Gy in both arms. Machine occupancy with CPAP (3–4 min) was 65% lower than ABC-DIBH (10 min). All patients demonstrated full compliance, with no setup delays, no adverse events, and 100% willingness to repeat CPAP. EORTC QLQ-C30 confirmed preserved global health, functional domains, and zero dyspnoea scores.

Conclusion:

CPAP provides substantial, reproducible cardiac and LAD dose reduction, with consistent benefit across all treatment complexities including IMC, without compromising lung constraints. A 65% reduction in machine occupancy, combined with excellent patient compliance and satisfaction, establishes CPAP as a feasible, scalable, and resource-efficient cardiac-sparing strategy, particularly suitable for high-volume and resource-limited settings. Larger comparative trials against DIBH are warranted.