OBJECTIVES: Variability in the breathing pattern of cancer patients 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 left breast anterior-posterior displacement was measured using an Osiris surface-image mapping system.
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 to their spontaneous breathing pattern. During mechanical ventilation, the mean amplitude of left breast marker displacement was 5 ± 1mm, the mean variability in its peak inflation position was 0.5 ± 0.1 mm and that in its trough inflation position was 0.4 ± 0.0 mm. Their mean drifts were not significantly different from zero (peak drift was -0.1 ± 0.2 mm/min and trough drift was -0.3 ± 0.2 mm/min). Patients had normal resting mean systolic blood pressure (131 ± 5 mmHg) and mean heart rate (75 ± 2 b.p.m.) before mechanical ventilation. During mechanical ventilation mean blood pressure did not change significantly, mean heart rate fell by 2 b.p.m. (p<0.05) with preoxygenation and rose by only 4 b.p.m. (p<0.05) during preoxygenation with hypocapnia. No patients reported discomfort and all 15 were always willing to return to the laboratory on multiple occasions to continue the study.
CONCLUSIONS: This simple technique for regularizing breathing may have important applications in radiotherapy. Advances in knowledge: Variations in breathing pattern introduce major problems in imaging and radiotherapy planning and delivery and are currently addressed to only a limited extent by asking patients to breathe to auditory or visual guidelines. We provide the first demonstration that a completely different technique, of using a mechanical ventilator to take over the patients breathing for them, is easy for conscious and unsedated patients and reduces the within-patient variability of breathing. This technique has potential advantages in radiotherapy over currently used breathing guidance interventions because it does not require any active participation from, or feedback to the patient and is therefore worthy of further clinical evaluation.