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Thesis
The dosimetric impacts of gated radiation therapy and 4D dose calculation in lung cancer patients
University of Iowa
Master of Science (MS), University of Iowa
Autumn 2014
DOI: 10.17077/etd.dnws-yhjf
Abstract
<p>With the introduction of four dimensional-computed tomography (4DCT), treatment centers are now better able to account for respiration-induced uncertainty in radiation therapy treatment planning for lung cancer. We examined two practices in which 4DCT is used in radiotherapy. Our first study investigated the dosimetric uncertainty in four-dimensional (4D) dose calculation using three temporal probability distributions: 1) uniform distribution, 2) sinusoidal distribution, and 3) patient-specific distribution derived from the respiratory trace. Four-dimensional dose was evaluated in nine lung cancer patients. First, dose was computed for each of 10 binned CTs using 4DCT and deformable image registration. Next, the 10 deformed doses were summed together using one of three temporal probability distributions. To compare the two approximated 4D dose calculations to the 4D calculation derived using the patient's respiratory trace, 3D gamma analysis was performed using a tolerance criteria of 3% dose difference and 3mm distance to agreement. Additionally, mean lung dose (MLD), mean tumor dose (MTD), and lung V20 were used to assess clinical impact. For all patients, both uniform and sinusoidal dose distributions were found to have an average gamma passing rate >99% for both the lung and PTV volumes. Compared with 4D dose calculated using the patient respiratory trace, uniform distribution and sinusoidal distribution showed a percentage difference on average of -0.1±0.6% and -0.2±0.4% in MTD, -0.2±2.0% and -0.2±1.3% in MLD, 0.9±2.8% and -0.7±1.8% in lung V20, respectively. We concluded that 4D dose computed using either a uniform or sinusoidal temporal probability distribution is able to approximate 4D dose computed using the patient-specific respiratory trace.</p>
<p>Our second study evaluated the dosimetric and temporal effects of respiratory gated radiation therapy using four different gating windows (20EX-20IN, 40EX-40IN, 60EX-60IN, and 80EX-80IN) and estimated the corresponding treatment delivery times for normal (500MU/min) and high (1500MU/min) dose rates. Five patients (3 non-gated, 2 gated 80EX-80IN) were retrospectively evaluated. For each patient, four individual treatment plans corresponding to the four different gating windows were created, and treatment delivery time for each plan was estimated using a MATLAB (MathWorks, Natick, MA) algorithm. Results showed that smaller gating windows reduced PTV volume, mean lung dose, and lung V20, while maintaining mean tumor dose and PTV coverage. Treatment times for gated plans were longer when dose rate was unchanged, however, increased dose rates were shown to achieve treatment times comparable to or faster than non-gated delivery times. We concluded that gated radiation therapy in lung cancer patients could potentially reduce lung toxicity, while as effectively treating the target volume. Furthermore, increased dose rates with gated radiation therapy are able to provide treatment times comparable to non-gated treatment.</p>
Details
- Title: Subtitle
- The dosimetric impacts of gated radiation therapy and 4D dose calculation in lung cancer patients
- Creators
- Ouided Rouabhi - University of Iowa
- Contributors
- Junyi Xia (Advisor)Joseph M. Reinhardt (Committee Member)Ryan T. Flynn (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Biomedical Engineering
- Date degree season
- Autumn 2014
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.dnws-yhjf
- Number of pages
- xii, 61 pages
- Copyright
- Copyright © 2014 Ouided Rouabhi
- Language
- English
- Date submitted
- 03/08/2019
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 59-61).
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering
- Record Identifier
- 9983776929502771
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