Semester of Graduation

Spring 2019


Master of Science (MS)


Physics and Astronomy

Document Type



Background: Respiratory motion affects all tumor sites in the thorax and abdomen. Variations of the respiratory pattern cause variations of the tumor motion which can result in differences between the planned and delivered dose distributions. Previous breathing guidance techniques have been investigated to improve respiratory reproducibility; however, ventilation assistance has not been investigated. We evaluated using bi-level positive airway pressure (BIPAP) ventilation assistance for improving respiratory reproducibility in patients with tumor sites impacted by respiratory motion.

Methods: Written informed consent was obtained for 10 patients currently undergoing radiation therapy treatment. Patients participated in sessions over their course of treatment, which occurred either before or after their radiation treatments. We collected and analyzed unassisted free- breathing (FB) and BIPAP ventilation-assisted respiratory volume data using spirometry. Patients used two BIPAP ventilators which both aimed to deliver the same volume of air each breath (i.e. tidal volume); however, one permitted patient triggering (i.e. permitted patients to initiate each breath) and the other did not. Intra-session and inter-session variation metrics were calculated for each patient using the platform-specific (i.e. FB or BIPAP) tidal volumes. We compared variation metrics between the platforms using the Wilcoxon signed-rank test, with a level of significance of 0.05.

Results: The BIPAP ventilator which permitted patient triggering was well tolerated; however, the other was not as well tolerated. Both BIPAP ventilators significantly reduced the intra-session tidal volume variation (p = 0.022 and p = 0.007) compared to FB. Neither of the BIPAP ventilators significantly reduced the inter-session tidal volume variation compared to FB (p = 0.203 and p = 0.074).

Conclusions: Based on the high correlation of tidal volume to tumor motion, any reduction of the tidal volume variation could result in a reduction of the tumor motion variation. Future work will include an investigation into the possible clinical benefits of using BIPAP ventilation assistance to reduce tumor motion variations.

Committee Chair

Fontenot, Jonas