Dissertation/Thesis Abstract

A Study on the Geometrical Limits and Modern Approaches to External Beam Radiotherapy
by Kopchick, Benjamin, Ph.D., The George Washington University, 2020, 171; 28025054
Abstract (Summary)

Radiation therapy is integral to treating cancer and improving survival probability. Improving treatment methods and modalities can lead to significant impacts on the life quality of cancer patients. One such method is stereotactic radiotherapy. Stereotactic radiotherapy is a form of External Beam Radiotherapy (EBRT). It delivers a highly conformal dose of radiation to a target from beams arranged at many different angles. The goal of any radiotherapy treatment is to deliver radiation only to the cancerous cells while maximally sparing other tissues. However, such a perfect treatment outcome is difficult to achieve due to the physical limitations of EBRT. The quality of treatment is dependent on the characteristics of these beams and the number of angles of which radiation is delivered. However, as technology and techniques have improved, the dependence on the quality of beams and beam coverage may have become less critical.

This thesis investigates different geometric aspects of stereotactic radiotherapy and their impacts on treatment quality. The specific aims are: (1) To explore the treatment outcome of a virtual stereotactic delivery where no geometric limit exists in the sense of physical collisions. This allows for the full solid angle treatment space to be investigated and to explore if a large solid angle space is necessary to improve treatment. (2) To evaluate the effect of a reduced solid angle with a specific radiotherapy device using real clinical cases. (3) To investigate how the quality of a single beam influences treatment outcome when multiple overlapping beams are in use. (4) To study the feasibility of using a novel treatment method of lattice radiotherapy with an existing stereotactic device for treating breast cancer. All these aims were investigated with the use of inverse planning optimization and Monte-Carlo based particle transport simulations.

For aim (1), multiple simulations of radiotherapy treatments were created by positioning beams on the surface of a sphere to cover a solid angle up to 4π steradians. Plans were optimized, and dosimetric criteria compared between the plans. Additionally, for aim (1), multi-leaf collimation was used to shape beams to a target volume. Results showed minimal improvements when increasing the solid angle space. The clinical benefit of a reduced solid angle treatment space is presented in (2). Here, using a device-specific to treating breast cancer, it is shown how critical structures can be beneficiaries of fewer beam angles.

Aim (3) was explored by optimizing plans using varying degrees of beam quality. Beam quality was adjusted by changing beam geometric penumbra. Results show that in the case of stereotactic radiotherapy, the overlapping of multiple isocenter focal spots of radiation can create a conformal distribution.

In aim (4), comparisons between simulation and experiment were conducted to explore the use of lattice radiotherapy in the breast. This final investigation resulted in a positive outlook for lattice radiotherapy, showcasing its feasibility to treat and manage large breast tumors.

Through investigating the geometric means of a radiotherapy apparatus, we show how limiting factors can be overcome or are not necessary for improving treatment outcomes. These aims can help direct the future development of radiotherapy techniques.

Indexing (document details)
Advisor: Yu, Cedric, Qiu, Xiangyun
Commitee: Reeves, Mark, Zeng, Chen, Downie, Evangeline, Cifter, Gizem
School: The George Washington University
Department: Physics
School Location: United States -- District of Columbia
Source: DAI-B 82/3(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Physics, Oncology, Biomedical engineering
Keywords: Radiotherapy, Stereotactic, Treatment quality
Publication Number: 28025054
ISBN: 9798664792355
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