Reducing the within-patient variability of breathing for radiotherapy delivery in conscious, unsedated cancer patients using a mechanical ventilator

Abstract

Objective: Variability in the breathing pattern of patients with cancer during radiotherapy requires mitigation, including enlargement of the planned treatment field, treatment gating and breathing guidance interventions. Here, we provide the first demonstration of how easy it is to mechanically ventilate patients with breast cancer while fully conscious and without sedation, and we quantify the resulting reduction in the variability of breathing. Methods: 15 patients were trained for mechanical ventilation. Breathing was measured and the left breast anteroposterior displacement was measured using an Osiris surface-image mapping system (Qados Ltd, Sandhurst, UK). Results: Mechanical ventilation significantly reduced the within-breath variability of breathing frequency by 85% (p,0.0001) and that of inflation volume by 29% (p,0.006) when compared with their spontaneous breathing pattern. During mechanical ventilation, the mean amplitude of the left breast marker displacement was 56 1mm, the mean variability in its peak inflation position was 0.560.1mm and that in its trough inflation position was 0.460.0mm. Their mean drifts were not significantly different from 0mmmin21 (peak drift was 20.16 0.2mmmin21 and trough drift was 20.360.2mmmin21). Patients had a normal resting mean systolic blood pressure (13165mmHg) and mean heart rate [7562 beats per minute (bpm)] before mechanical ventilation. During mechanical ventilation, the mean blood pressure did not change significantly, mean heart rate fell by 2bpm (p,0.05) with pre-oxygenation and rose by only 4bpm (p,0.05) during pre-oxygenation with hypocapnia. No patients reported discomfort and all 15 patients were always willing to return to the laboratory on multiple occasions to continue the study. Conclusion: This simple technique for regularizing breathing may have important applications in radiotherapy.