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 5 ± 1 mm, 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 0 mm min−1 (peak drift was −0.1 ± 0.2 mm min−1 and trough drift was −0.3 ± 0.2 mm min−1). Patients had a normal resting mean systolic blood pressure (131 ± 5 mmHg) and mean heart rate [75 ± 2 beats per minute (bpm)] before mechanical ventilation. During mechanical ventilation, the mean blood pressure did not change significantly, mean heart rate fell by 2 bpm (p < 0.05) with pre-oxygenation and rose by only 4 bpm (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.Advances in knowledge:Variations in the 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 patients who are conscious and unsedated 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.

Safely prolonging single breath-holds to >5 min in patients with cancer; feasibility and applications for radiotherapy

“…But, we believe that most patients will find voluntary hyperventilation too difficult, whereas we know they find mechanical hyperventilation straightforward. 19 This fact, in combination with the time required for final positioning, staff leaving the room and beam delivery checks for setup, indicates to us that if single and prolonged breath-holds have widespread application in radiotherapy, resources would be best applied to develop mechanical rather than voluntary hyperventilation. Furthermore, single prolonged breath-holds would have no detrimental effects on clinical efficiency, since all training could be achieved by non-radiotherapy staff at a separate location for as long as necessary for each patient.…”

“…BP, blood pressure; ECG, electrocardiography; PCO 2 , partial pressure of carbon dioxide; SpO 2 , oxygen saturation. Reproduced from Parkes et al 19 with permission from The British Institute of Radiology.…”

“…Thenceforth, the marker positions were recorded continuously to derive their x , y and z positions to the nearest 0.1 mm. 19 We then repeated the breath-hold following pre-oxygenation and hypocapnia (Table 2, order 6).…”

Mitigating Respiratory Motion in Radiation Therapy: Rapid, Shallow, Non-invasive Mechanical Ventilation for Internal Thoracic Targets

“…Here, non-invasive mechanical ventilation safely, easily and comfortably takes over breathing of the conscious, unmedicated patient, delivering with regularity the same respiratory minute ventilation but with an increased ventilation frequency and a reduced inflation volume for periods sufficient to image and deliver radiotherapy. [8]. However, a reduction in internal respiratory motion has not yet been investigated.…”

Prolonging deep inspiration breath-hold time to 3 min during radiotherapy, a simple solution

“…Firstly, ease of use is higher compared to the mechanical ventilator. As described by Parkes et al, the ventilator parameters need to be adapted to the volunteer [28] , and this requires training for appropriate operation. Secondly, set-up of the mechanical ventilator takes significantly longer and is prone to failure since an air-tight fit of the face mask is essential [29] .…”