Identifier

etd-11092008-142649

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

The purpose of this project was to investigate the interplay between gating window characteristics and target margin required to compensate for residual motion during the gating window. This project investigated the accuracy of ExacTrac and 4DCT imaging localizing an implanted coil at various phases of respiration. Radiochromic film measured delivered dose patterns for selected gating intervals over a variety of respiratory patterns. In order to establish accurate dosimetry, this project implemented and tested an EBT radiochromic film dosimetry system. Film testing showed that the performance of a medical grade Vidar Dosimetry Pro radiographic film scanner and an Epson V700 Photo flatbed scanner were very similar. Both scanners showed nearly the same performance in terms of measurement repeatability, noise, vertical and horizontal uniformity over a range of doses from 11.5-511.9 cGy. The Vidar was selected for these studies due to clinical availability. Even at the greatest coil velocities observed, ExacTrac coil localization agreed with calculated coil motion to within 0.8 mm. 4DCT showed errors up to 5.5 mm resolving coil position during large respiratory-induced velocities. 4DCT accurately measured the coil length within 1 mm of actual coil length at end expiration/inhalation. 4DCT can provide an accurate representation of the phantom at end-respiration for treatment planning purposes, and ExacTrac can accurately localize the coil to determine target motion in all phases For patient treatments it is suggested that target margins should be set using the residual motion during gating. For patients without implanted coils, the residual motion can be computed based on the target motion measured from 4DCT and the size of the gating window. For patients with implanted coils, the ExacTrac system can be used to directly measure residual tumor motion during gating. The hypothesis of this work was that gated delivery combined with 4DCT could limit internal margins to less than 3 mm while maintaining 95% prescription dose coverage of moving targets. The hypothesis was found to be true for gating windows of 10% and 20% for target motions up to 25 mm and was true with gating windows up to 50% for smaller motions (5 & 10 mm).

Date

2008

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Brent Parker

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