Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biomedical Engineering

Supervisor

Fenster, Aaron

Abstract

Treatment of gynaecological cancers often includes a type of conformal radiotherapy, known as brachytherapy, that allows radiation sources to be placed close to or directly into cancerous tissues, tailoring the dose to the local region around tumours and sparing surrounding normal tissues. These sources can be positioned via intracavitary applicators that are placed inside the vagina/uterus or interstitial implants, involving the insertion of multiple needles into the tissue. There is currently no standard imaging modality to visualize these applicators and needles at the time of placement, which would allow for the immediate assessment and refinement of the implant positions. Ultrasound (US), including three-dimensional (3D) US, is an inexpensive modality that offers many advantages for intraoperative imaging. The objective of this thesis was to develop and evaluate systems and methods for incorporating US guidance and implant location verification intraoperatively for brachytherapy treatment of gynaecological cancers.

Two 3D US imaging systems were developed and their utility for needle location verification was assessed. The geometric accuracy of the image reconstruction was validated for each system and preliminary feasibility studies were conducted in phantoms. The first system used a 3D side-fire transrectal ultrasound (TRUS) approach and was found to provide good visualization of the needles for five patients. The second system used a 360° 3D side-fire transvaginal ultrasound (TVUS) approach to provide clear visualization of the needle trajectories and surrounding anatomical features, in a study of six patients. To provide real-time feedback during insertion, a generalized deep learning-based segmentation method was implemented and applied to two-dimensional TVUS images, accurately localizing the needles. To aid in interpretation of the 3D TVUS images, a 3D needle segmentation approach was also implemented, providing additional information about the needle positions relative to each other. The 3D US imaging techniques were extended to intracavitary/hybrid applicators in a phantom study to assess the feasibility of fusing 3D TRUS images with 3D transabdominal US images, providing more comprehensive visualization of the applicators and surrounding anatomy. These US imaging tools have the potential to improve the quality of gynaecological brachytherapy treatment by providing accessible and versatile systems for intraoperative implant assessment.

Summary for Lay Audience

Gynaecological cancers are cancers that begin in parts of a woman’s reproductive system, such as the vagina or cervix. They are often treated using high doses of radiation to kill the cancer cells. This radiation can be given from inside the body (called brachytherapy) by placing devices in the vagina or inserting needles into the tumours. To reduce side-effects and give the best treatment, these devices or needles, called applicators, must be placed in the correct locations. Medical images are a useful way to check that the applicators are in the correct place. Often three-dimensional (3D) images are better than two-dimensional (2D) images for deciding if the applicators are placed correctly but 3D systems may be costly. One imaging type that is commonly available is ultrasound (US). The goal of this work was to create 3D US tools to help doctors decide if applicators are placed correctly.

Two ways of creating 3D US images were tested. These systems use motors to turn a normal 2D US probe and send the 2D images to a computer where they are built into 3D images. The first way creates images by turning the US probe in the patient’s rectum. The needles could be seen in these images for five patients. The second way turned the US probe in a full circle inside the vagina so that needles on all sides could be seen. The needle paths and nearby organs, such as the bladder, could be seen in the images from six patients. To help doctors quickly decide if the needles are in the correct places, two computer programs were created to show where the needles were in both 2D and 3D US images. Lastly, 3D US images were taken of a model representing the human body. These images were used to decide if 3D US images taken from the rectum and the belly could be combined to see more of the applicators than with one image type. These US tools may help doctors check that applicators are placed correctly in the future, making this type of treatment easier, safer, and available to more women.

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