Dissertation
Needle free cervical cancer treatment with 169YB-based rotating shield brachytherapy
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2020
DOI: 10.17077/etd.005616
Abstract
Helical intracavitary rotating shield brachytherapy (RSBT) is presented as a means of achieving asymmetrical dose distributions in cervical cancer high-dose-rate brachytherapy (HDR-BT) treatments. Intracavitary/interstitial (IC/IS) brachytherapy is commonly used to create asymmetrical dose distributions and to treat large high-risk clinical target volumes (HR-CTVs), but the addition of interstitial needles can increase treatment time. Additionally, IC/IS is not widely available and there is a lack of IC/IS expertise in the U.S. Due to the partial shielding inside the applicator, an isotope with a lower average energy than the commonly used HDR-BT isotope, 192Ir is needed for treatment. In this work, an intracavitary-only, multi-shield RSBT applicator that uses 169Yb is presented. In order to model the patient-specific dose distributions for the shielded applicator in treatment plans, Monte Carlo modeling was performed to develop dose distributions for several RSBT applicators, including a universal model capable of interfacing with existing afterloaders on the market, and the final RSBT model, which is vendor-specific and uses a Source Production and Equipment Company (SPEC), Inc. (St. Rose, LA) 169Yb source that has been lengthened to allow for re-activation after initial decay. Distributions were also created for the two emission angles that the applicator uses, 45° and 180°. Additional Monte Carlo models for treatment planning simulations were created to aid in the comparison of RSBT to other intensity-modulated brachytherapy techniques.
In a 37-patient treatment planning study, multi-shield RSBT was able to reduce treatment times compared to intracavitary/interstitial (IC/IS) brachytherapy, while meeting the 85 Gy planning goal in 86% of plans. In a second treatment planning study, 169Yb-based RSBT provided better results than 169Yb-based DMBT and 192Ir-based RSBT and DMBT, demonstrating the advantages of the RSBT design and the use of the 169Yb isotope. Error tolerance testing was performed on the RSBT applicator to measure the effect of applicator shift and rotation on the dose to bladder, rectum, sigmoid, and HR-CTV. The tolerance was found to be ±1.5 mm and ±5° in order to maintain an error of less than 10% to all organs and HR-CTV. The applicator shift tolerance was found to be similar to the tolerance for IC, thus demonstrating that the tolerance with respect to applicator shift is not affected by the novel partial shielding.
In conclusion, helical multi-shield RSBT shows promise as a means to replace IC/IS for patients with large or laterally-extended HR-CTVs, and its intracavitary only design reduces the need for interstitial needles. The tolerance associated with the RSBT system is acceptable, thus improving the argument that RSBT could provide strong benefits for cervical cancer HDR treatments.
Details
- Title: Subtitle
- Needle free cervical cancer treatment with 169YB-based rotating shield brachytherapy
- Creators
- Karolyn M. Hopfensperger
- Contributors
- Ryan T Flynn (Advisor)Joseph M Reinhardt (Committee Member)Yusung Kim (Committee Member)Sarah C Vigmostad (Committee Member)Xiaodong Wu (Committee Member)Weiyu Xu (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Engineering
- Date degree season
- Summer 2020
- DOI
- 10.17077/etd.005616
- Publisher
- University of Iowa
- Number of pages
- xiv, 76 pages
- Copyright
- Copyright 2020 Karolyn M. Hopfensperger
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 68-76).
- Public Abstract (ETD)
Brachytherapy is a form of radiation therapy that is commonly used to treat locally-advanced cervical cancer. It uses a radioactive isotope that travels inside the uterus to deliver radiation to the cervix and vagina. Traditional brachytherapy relies on the 192Ir isotope, which has a high average energy and an isotropic dose distribution. In order to treat large or laterally-extended tumors using brachytherapy, the addition of interstitial needles is necessary, but the placement of the needles can increase treatment time and cause patient discomfort. Helical, multi-shield, rotating shield brachytherapy (RSBT) is proposed to deliver high doses to the tumor without the need for needles. In this work, the feasibility of RSBT as a means to treat locally-advanced cervical cancer is determined. In the first part of this work, models of the RSBT applicator are tested to ensure that they can deliver the appropriate dose distributions, and a treatment planning study is performed to compare RSBT using the 169Yb isotope to intracavitary/interstitial brachytherapy. The tolerance of the system is determined in order to prevent overdoses to nearby organs or underdoses to the tumor volume. In the final part of this work, RSBT is compared to several treatment methods using different isotopes.
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering
- Record Identifier
- 9983988198202771
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