Program Information
Assessment of Breath-Hold Volume Inconsistencies with the Active Breathing Coordinator System as a Function of Inhalation Rate
L Padilla1*, P Bardos1 , T Kim1 , (1) Virginia Commonwealth University, Richmond, VA
Presentations
MO-RAM-GePD-T-1 (Monday, July 31, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge
Purpose: To quantify the variation in Active Breathing Coordinator (ABC) breath-hold volumes based on inhalation rate and to verify that volumes recorded by the system match the measured reference. These findings were used to develop corrections for ABC breath-hold volumes recorded by the system.
Methods: A calibrated 3L air cylinder with markings every 0.08L was connected to the ABC system (Elekta) through an air-tight plastic connector. A total of 113 breath-holds with different breath-hold thresholds (0.5-2.5L, in 0.5L increments) were performed using the cylinder to mimic respiration. The cylinder piston was controlled at different inhalation rates to study the effects of air speed on the volume reading. Air volume, as given by the physical cylinder markings (CMvol), was recorded for each breath-hold (“ground truth”). ABC output files were analyzed to obtain the volume measured per breath-hold (ABCvol), and the inhalation rate in the 0.5s interval before breath-hold. The two sets of volumes were compared and the effects of inhalation rate on breath-hold volume were analyzed.
Results: ABCvols showed an increase with inhalation rate. CMvols also showed an increase, although with a higher inhalation rate onset and not as pronounced. ABCvols were systematically higher than the CMvols by an average of 0.11L. The discrepancy between the two increased with inhalation rate (spirometer fan has higher momentum-systematically overestimates). Three volume correction polynomial fits based on ABCvols versus CMvols were derived for threshold bins of 0.5L, >0.5L to =1L (R-squared values of 0.97, 0.94, and 0.95, respectively).
Conclusion: Volumes recorded by the ABC system are overestimated, but breath-hold volumes are in fact higher for faster inhales based on our results. These corrections will provide more accurate data than the uncorrected ABC output values when conducting breath hold reproducibility studies or performance comparisons with other respiratory motion management techniques like surface imaging.
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