Rapid Mechanical Ventilation Superior to Rapid Jet Ventilation for Diaphragm Motion Reduction in Radiotherapy

Abstract

To account for respiratory motion in radiotherapy either large target volumes are defined, or patients are instructed to breath-hold repeatedly. Alternatively, non-invasive ventilation induced regularized breathing at high frequencies may reduce motion, minimizing irradiated volumes. We quantified the motion of the right hemidiaphragm during rapid non-invasive mechanical ventilation (NI-MV) and rapid non-invasive jet ventilation (JET) to compare the effectiveness on respiratory motion. After ethics committee approval and written informed consent, 15 healthy volunteers enrolled in this study. During a first session, they were trained being ventilated with NI-MV and JET to regularize their breathing. The ventilation frequencies under investigation included 60 breaths per minute (brpm) NI-MV (60NI-MV), and 60, 150, 250 and 400 brpm JET (60JET, 150JET, 250JET and 400JET, respectively). In a second session, ultrasound movies of 40 sec (temporal resolution 23 Hz) were acquired in the sagittal plane twice for each ventilation frequency. We quantified the magnitude of ventilation-induced rhythmic motion as the mean distance between each subsequent end-inspiration and end-expiration position of the diaphragm. Also, we determined the overall maximum motion of the diaphragm over the 40 sec measurement. We tested for statistically significant differences between median rhythmic motion and overall maximum motion during all frequencies (paired Wilcoxon's tests (n = 10); corrected p-value for multiple testing (p = 0.05/N)). All volunteers were successfully trained. There were no significant differences between repeated measurements of each ventilation frequency; hence we pooled the data. We found that 60NI-MV resulted in significantly smaller rhythmic motion compared to 60JET (median 5.0 mm and 8.9 mm respectively; p<0.001). Higher ventilation frequencies with JET decreased the median rhythmic motion magnitude (2.3 mm, 1.0 mm and 0.5 mm at 150JET, 250JET and 400JET respectively; p<0.001). However, during these higher frequencies the smaller rhythmic motion magnitudes did not result in smaller overall maximum motion compared to 60NI-MV. The median overall motion was 17.2 mm, 15.8 mm and 13.4 mm for 150JET, 250JET and 400JET respectively (p<0.005 only between 60JET and 400JET). The overall maximum motion during 60NI-MV was significantly smaller compared to 60JET (12.3 mm and 24.1 mm respectively; p<0.001). The US movies clearly showed that volunteers superimposed spontaneous breathing on top of JET. Finally, volunteers indicated NI-MV to be more comfortable than JET. Mechanical ventilation at 60 brpm maximally reduced the overall motion of the right hemidiaphragm and was more comfortable than jet ventilation. Therefore, mechanical ventilation appears to be superior to control respiratory motion for radiotherapy.