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

Abstract

Reducing respiratory motion during the delivery of radiation therapy reduces the volume of healthy tissues irradiated and may decrease radiation-induced toxicity. The purpose of this study was to assess the potential for rapid shallow non-invasive mechanical ventilation to reduce internal anatomy motion for radiation therapy purposes. Ten healthy volunteers (mean age, 38years; range, 22-54years; 6 female and 4 male) were scanned using magnetic resonance imaging during normal breathing and at 2 ventilator-induced frequencies: 20 and 25 breaths per minute for 3minutes. Sagittal and coronal cinematic data sets, centered over the right diaphragm, were used to measure internal motions across the lung-diaphragm interface. Repeated scans assessed reproducibility. Physiologic parameters and participant experiences were recorded to quantify tolerability and comfort. Physiologic observations and experience questionnaires demonstrated that rapid shallow non-invasive ventilation technique was tolerable and comfortable. Motion analysis of the lung-diaphragm interface demonstrated respiratory amplitudes and variations reduced in all subjects using rapid shallow non-invasive ventilation compared with spontaneous breathing: mean amplitude reductions of 56% and 62% for 20 and 25 breaths per minute, respectively. The largest mean amplitude reductions were found in the posterior of the right lung; 40.0mm during normal breathing to 15.5mm(P<.005) and 15.2mm(P<.005) when ventilated with 20 and 25 breaths per minute, respectively. Motion variations also reduced with ventilation; standard deviations in the posterior lung reduced from 14.8mm during normal respiration to 4.6mm and 3.5mm at 20 and 25 breaths per minute, respectively. To our knowledge, this study is the first to measure internal anatomic motion using rapid shallow mechanical ventilation to regularize and minimize respiratory motion over a period long enough to image and to deliver radiation therapy. Rapid frequency and shallow, non-invasive ventilation both generate large reductions in internal thoracic and abdominal motions, the clinical application of which could be profound-enabling dose escalation (increasing treatment efficacy) or high-dose ablative radiation therapy.