When using highly conformal radiotherapy techniques, such as proton therapy, a controlled breathing pattern and a minimal breathing amplitude could greatly benefit the treatment of mobile tumors. This reduction in tumor motion may be achieved with the use of a ventilator that is able to regulate and modulate the breathing pattern. CPAP provides a constant level of positive airway pressure. Compared to spontaneous breathing, the use of CPAP increased lung volume and can result in a significant decrease in tumor movement and a significant decrease in both mean lung and mean heart radiation dose. These results were found in patients treated for limited stage disease, it is not clear if this approach is feasible for patients with more advanced stage of disease that undergo radiotherapy with curative intent.

With Bilevel Positive Airway Pressure (BiPAP), tidal volume excursions are determined by the pressure difference between the set inspiratory positive airway pressure (IPAP) and the set expiratory positive airway pressure (EPAP). This mode of ventilation increases lung volume comparable to CPAP, but also to control tidal volumes and breathing frequency. However, BiPAP has never been studied in the setting of motion mitigation during radiotherapy and BiPAP might be more difficult to adjust to for patients compared to CPAP. Therefore, the current study is proposed to evaluate whether or not CPAP or BiPAP is of benefit in patients that undergo radiotherapy for larger intra-thoracic tumor volumes.

The study will follow a 2-step approach.

First (Phase 1, n=10), the feasibility of short-term use of CPAP and BiPAP and its effects on (regional) lung volumes, tidal volumes and breathing frequency will be investigated in patients with intra-thoracic tumors who are planned for radiotherapy. This is necessary to select the best setting of CPAP or BiPAP with which minimal tumor motion is expected (and that is feasible for the patient).

In the second phase (n=21), the particular setting found in fase 1 is investigated: weekly repeated radiotherapy planning (4D) CT scans with and without CPAP/BiPAP will be aquired to evaluate the influence on tumor motion and dose to the target and organs at risk. Radiotherapy will be deliverd according to local protocol without the use of CPAP/BiPAP.

Inclusion Criteria:

• Age ≥18 years
• Stage III/IV (N)SCLC, esophageal cancer or malignant lymphoma that will be treated with curative intent
• WHO 0-2.
• Written informed consent

Exclusion Criteria:

• Facial deformations so that facial mask is impossible to fit
• Noncompliance with any of the inclusion criteria.
• Planned for radiotherapy with fraction dose ≥3 Gy.
• Severe heart failure (LVEF<30%)