A phase II trial to determine the proportion of patients where the use of continuous positive airway pressure (CPAP) results in a superior radiation plan compared to standard planning procedures. The rationale for using CPAP with radiotherapy is based on its ability to increase the tidal volume, flatten the diaphragm thus reducing respiratory excursions.The resultant lung hyperinflation and reduced respiratory excursions can be harnessed for radiotherapy purposes by:

1. Displacing the heart away from the radiotherapy field
2. Reducing the volume of functional lung irradiated
3. Reducing the radiotherapy target motion

CPAP has been shown to be superior to free breathing radiotherapy (RT), however it remains unclear how much benefit it confers vs other motion management adjuncts such as deep inspiration breath hold (DIBH) or 4-DCT.

PRIMARY OBJECTIVE:

To determine the proportion of patients where the use of CPAP results in a superior radiation plan compared to standard planning procedures in each patient cohort

SECONDARY OBJECTIVES

To determine:

• Impact of CPAP on treatment delivery time;
• Impact of CPAP on total lung volume;
• CPAP compliance;
• Patient experience;

Breast-specific:

• Comparison of organ at risk (OAR) dose constraints between CPAP and deep DIBH)

SABR-specific:

• Internal target volume (ITV) reduction;
• OAR dose constraints between CPAP and standard planning procedures.

Breast cancer patients will undergo normal free breathing and DIBH radiotherapy planning scans. An additional scan with CPAP will be done for the purpose of the study. Radiotherapy plans will be produced on both the DIBH and CPAP planning scans. The planning scan with the best dosimetry will be chosen for treatment. If CPAP has a better radiation plan, then the patient will have CPAP administered during their daily RT. The DIBH plans for each patient, will serve as controls SABR patients will undergo the standard 4-D or breath hold CT and then CPAP CT for the purpose of the study. Respiratory movements will be monitored by Varian RPM system. Radiotherapy plans will be produced from the standard CT and the CPAP CT for comparison.

Patients will be treated on the best plan The trial aim to recruit 70 patients with invasive carcinoma of the breast undergoing adjuvant radiotherapy that includes breast/chest-wall plus regional lymph nodes, and a convenient sample size of those undergoing SABR to lung or liver

Inclusion Criteria:

• Any patient with pathologically-confirmed invasive breast cancer and planned for adjuvant radiotherapy to the breast or chest-wall with regional lymph node coverage
• Any patient deemed suitable for lung or liver SABR as per departmental guidelines
• Must have signed written informed consent

Exclusion Criteria:

• Cannot tolerate CPAP e.g due to severe claustrophobia
• Re-irradiation