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

Purpose: 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. Methods and Materials: Ten healthy volunteers (mean age, 38 years; range, 22-54 years; 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 3 minutes. 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. Results: 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; 40.0 mm during normal breathing to 15.5 mm (P < .005) and 15.2 mm (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 14.8 mm during normal respiration to 4.6 mm and 3.5 mm at 20 and 25 breaths per minute, respectively. Conclusions: 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. Crown Copyright (C) 2018 Published by Elsevier Inc. All rights reserved.