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The Use of 4D-MRI to Evaluate the Role of Continuous Positive Airway Pressure (CPAP) in Proton Therapy Motion Management
M Walb*, J Christopherson , C Hallemeier , S Holets , J Johnson , J Kruse , K McGee , T Meyer , D White , E Tryggestad , Mayo Clinic, Rochester, MN
Presentations
SU-I-GPD-J-54 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Breathing motion during proton therapy has deleterious dosimetric consequences; existing gating or breath-holding strategies limit treatment delivery efficiency. Here we evaluated the role of continuous positive airway pressure (CPAP) as an efficient breathing motion mitigation strategy for proton therapy.
Methods: Ten healthy volunteers were recruited for this IRB-approved study. Coronal 2D MR images were acquired on a 3T MR scanner (750W, GE Healthcare, Waukesha, WI) using a balanced steady-state free precession (bSSFP) sequence. 1D navigator profiles, positioned to monitor the liver craniocaudally, were interleaved between successive image frames. Retrospective analysis of these profiles for liver dome position, in conjunction with a timing log, allowed for sorting into amplitude probability respiratory bins using in-house software (MATLAB, MathWorks, Natick, MA) to generate DICOM 4D-MRI images. After acquiring baseline MR data, a certified respiratory technician administered CPAP using an MRI compatible ventilator (Hamilton MRI1, Hamilton Medical, Bonaduz, Switzerland; Respironics PerforMax, Philips, Amsterdam, Netherlands). MR images were then obtained under CPAP pressures of 10-14 and 8 cmH₂O, respectively. Short equilibration periods of approximately 4 minutes were inserted after each CPAP intervention prior to MRI acquisition. Liver dome excursion on 4D-MRI was used as a surrogate to quantify breathing motion.
Results: Six of the ten study subjects demonstrated increased respiratory motion with the use of the CPAP device relative to baseline. Of the four volunteers that showed a reduction in breathing motion extent with CPAP, three demonstrated the least motion at the lower pressure (8 cmH₂O). The mean reduction in diaphragmatic excursion (relative to baseline) of these four volunteers was 7.4 mm.
Conclusion: 4D-MRI is an effective tool in the noninvasive evaluation of motion management strategies. The use of CPAP for respiratory motion reduction was inconclusive. Further studies are needed to explore parameters such as CPAP pressure, incubation time, and biophysical variations among subjects.
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