Access Type

Open Access Dissertation

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Medical Physics

First Advisor

Thomas M. Guerrero

Second Advisor

Jay Burmeister

Abstract

This work investigates the use of High Frequency Percussive Ventilation as a technique for respiratory motion mitigation in radiotherapy. This technique was extensively investigated in several prospective and retrospective studies.

In an initial prospective study, we evaluated the feasibility of HFPV and chest-wall motion reduction, by recruiting 15 healthy volunteers to undergo HFPV with three commercially available interfaces. For direct tumor motion immobilization, a second prospective study was performed in which with ten lung cancer patients underwent HFPV while imaged with high frame rate fluoroscopy. Diaphragm motion and image artifacts were quantified in a prospective study of a healthy volunteer that underwent MRI while undergoing HFPV. Several retrospective studies were performed to quantify the interplay effects as well as gradient effects of HFPV vs. free breathing in photon and proton radiotherapy. Furthermore, a retrospective phantom study was performed for quantifying PTV volume reduction as well as doses to the organs at risk. Reproducibility of the HFPV was evaluated in a prospective study of five volunteers who underwent five sessions of HFPV in three different days. Lastly, as part of this study, a HFPV mask was designed and prototyped for better comfort, prolonged percussive time, minimal baseline drifting, as well as patient-controlled valve.

HFPV provides prolonged breath-hold like apnea in awake patients that could last as long as 16 minutes. In this first ever study, direct tumor motion was drastically reduced from > 10 mm to < 3mm. Similarly, diaphragm motion was reduced by as much as > 90 %. HFPV proved significantly beneficial in reducing effects of interplay in proton radiotherapy and photon dose gradient measurements, increasing gamma index by as much as 20 to 30 % from free breathing to HFPV. Similarly, hot and cold spots were reduced by > 50 %. HFPV is reproducible within < 2 mm both intra- and inter- fraction, but it can be further improved by applying minor adjustments to the pressure and frequency of the Percussionaire unit. Although further modifications will be made, the newly designed prototype provided less leakage and better comfort as well as providing patients with the direct ability to switch between room air and HFPV. HFPV is novel and promising technique for tumor immobilization in a radiotherapy setting.

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