Dissertation
Design, construction, validation, and integration of the dynamic collimation system for pencil beam scanning proton therapy
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007086
Abstract
Purpose: This work summarizes the development of a prototype energy-layer specific collimator, called the dynamic collimation system (DCS), to reduce the lateral penumbra of pencil beam scanning proton therapy treatments.
Methods: From a basic concept, we developed a prototype using an in-house Monte Carlo beam model to drive design decisions that would minimize lateral penumbra, such as range shifter characteristics and the use of dynamically focused collimators. Because the DCS is a removable accessory, we developed a quality control alignment system called the Central Axis Alignment Device (CAAD) to ensure alignment. Using TOPAS generated simple fields, EBT3 film and a MatriXX-PT IC array, treatment accuracy was quantified for a set of clinically representative deliveries where the automated positioning of the collimators was synchronized with the scanned position of the proton beam.
Results: We successfully designed and constructed the DCS to meet the required scientifically driven design decisions. Our control system was integrated with the IBA scanning controller to allow automated treatments with a low latency (<45 ms). Positional trimmer accuracy was verified to within 50 µm and the kinematics were tuned to be stable under gantry conditions up to an operating jerk value of 400 m/s^3. The CAAD aligns the collimators with respect to the field with an accuracy of less than 100 um. Mean dose reductions of 12% and 45% to the 10- and 30-mm rings surrounding a target were achieved in preliminary automated treatment deliveries.
Conclusion: This work signifies a significant milestone in the development of the DCS clinical prototype. The mechanical systems were successfully characterized and integrated within a commercial IBA scanning controller, enabling preliminary dosimetric studies for clinical treatments.
Details
- Title: Subtitle
- Design, construction, validation, and integration of the dynamic collimation system for pencil beam scanning proton therapy
- Creators
- Theodore Geoghegan
- Contributors
- Daniel Hyer (Advisor)John Buatti (Committee Member)Ryan Flynn (Committee Member)Sarah Gerard (Committee Member)Joseph Reinhardt (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Engineering
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007086
- Number of pages
- xiv, 101 pages
- Copyright
- Copyright 2023 Theodore Geoghegan
- Language
- English
- Date submitted
- 04/17/2023
- Date approved
- 04/25/2023
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 94-101).
- Public Abstract (ETD)
- Proton therapy can reduce normal tissue toxicity in cancer patients, but its maximum potential has not yet been fully realized due to limited lateral dose conformity. While the Bragg peak provides exceptional distal tissue sparing, in many cases, lateral tissue sparing is worse than that of photons. To combat this, collimators can be used to shape the beam along the tumor periphery, blocking the dose from spreading laterally into healthy tissue. There exist deficiencies with current collimation systems which must be improved to maximize plan quality for shallow and sensitive targets. As such, a critical need exists to develop a cost-effective and compact collimation system that can be added to existing protons therapy beamlines to improve lateral dose conformity. The Dynamic Collimation System (DCS) is our groups solution to this problem and consists of two pairs of orthogonal nickel collimating trimmers that move in synchrony with the proton pencil beam to intercept and effectively “trim” the pencil beam at the edge of the target, substantially reducing lateral dose spread. This project not only proposes to build a functional prototype, but also develop the requisite quality assurance devices and procedures to ensure safe and effective clinical use of the DCS. First was the design, construction, validation, and integration of the prototype DCS. Next was the design, construction, validation, and integration of the Central Axis Alignment Device. Lastly, we dosimetrically validated the DCS with measurements and exceeded gamma pass rates of over 95% for all collimated plans. The results of this work are a fully functioning collimation system and quality control alignment device that are ready for future experiments and development.
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering
- Record Identifier
- 9984428942102771
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