Purpose: To use implanted electromagnetic beacons to understand the effect of Continuous Positive Airway Pressure (CPAP) on the regularity and amplitude of respiration when undergoing thoracic radiation therapy.
Methods: This was an exploratory objective of an MLC tracking trial in patients receiving stereotactic ablative body radiotherapy for lung tumours. Electromagnetic beacons (Calypso, Varian Medical Systems) were endobronchially inserted in the lungs of eight patients receiving stereotactic ablative body radiotherapy for lung tumours. Beacon motion traces were acquired for four treatment fractions per patient under regular respiration (during radiation therapy). Subsequent to each fraction, CPAP was applied and the pressure was increased over 5-minutes from 5 cmH20 to 15 cmH20, after which beacon motion traces were recorded for 3 to 8 minutes. 3D motion vectors were assessed; the difference in mean respiratory period and motion amplitude were compared between regular respiration and CPAP traces.
Results: CPAP reduced the amplitude by (mean ± st.dev.) 1.0 ± 4.4 mm (range -4.6 to 11.5 mm); greater amplitude reduction was observed for larger breathing motions (Spearman rank ρ = 0.67). CPAP increased motion however in eighteen fractions in seven out of eight patients, although the increase in five of the fractions was under 1 mm. The mean respiratory period increased by 1.4 ± 2.1 seconds (range -6.7 to 2.3 seconds) when using CPAP. Five out of the eight patients had fewer breaths statistically considered outliers with the use of CPAP than with regular respiration, implying less erratic breathing.
Conclusion: While on average CPAP reduced respiratory motion most patients experienced an amplitude increase in at least one fraction. Motion reduction was maximised for patients with larger respiratory motion, indicating a subset who may benefit from CPAP for motion margin reduction. CPAP resulted in an increase in respiratory period and a decrease in erratic breaths.
Funding Support, Disclosures, and Conflict of Interest: Australian Government Research Training Program Scholarship - presenting author Study partially funded by Varian Medical Systems
Not Applicable / None Entered.