Background: Minimizing tumor motion decreases side-effects in radiotherapy for intra-thoracic tumors, as less motion ensures less radiation on healthy tissue. The use of Continuous or Bilevel Positive Airway Pressure (CPAP/BiPAP) could decrease breathing amplitudes and therefore tumor motion by increasing lung volumes, but the optimal setting is unknown.

Methods: In 10 patients (5 with lung cancer, 5 with other intra-thoracic tumors), CPAP/BiPAP was tested with the following settings for 10 minutes each: CPAP 5, 10 and 15 cmH₂O and BiPAP 14/10 cmH₂O with a low (7 breaths/min) and high back-up frequency (1 breath above the spontaneous breathing frequency). Electrical impedance tomography (EIT) was recorded to evaluate lung volumes. The global impedance signal of the EIT was used to analyze tidal impedance variation (TIV, i.e. impedance change during a tidal breath) as a measure of breathing amplitude.

Results: Nine out of ten patients tolerated all settings; one patient could not sustain CPAP 15 cmH₂O. As shown in Figure 1, CPAP 5 cmH₂O and BiPAP with a high back-up frequency lead to the lowest breathing amplitudes.

Conclusions: This is the first study to show the feasibility and use of CPAP/BiPAP on breathing amplitudes. Further research is conducted to investigate the effect of CPAP/BiPAP on tumor motion and its consequence on radiation to the target and surrounding healthy tissues.