Development and Validation of Tools for Improving Intraoperative Implant Assessment with Ultrasound during Gynaecological Brachytherapy
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.