High dose-rate brachytherapy is a typical part of the treatment process for cervical cancer. During this procedure, radioactive sources are placed locally to the malignancy using specialized applicators or interstitial needles. To ensure accurate dose delivery and positive patient outcomes, medical imaging is utilized intra-procedurally to ensure precise placement of the applicator. Previously, the fusion of three-dimensional ultrasound images has been investigated as an alternative volumetric imaging technique during cervical brachytherapy treatments. However, the need to manually register the two three-dimensional ultrasound images offline resulted in excessively large registration errors. To overcome this limitation, we have designed and developed a tracked, automated mechatronic system to inherently register three-dimensional ultrasound images in real-time. We perform a system calibration using an external coordinate system transform and validate the system tracking using a commercial optical tracker. The results of both experiments indicated sub-millimeter system accuracy, indicating the superior performance of our device. Future work for this study includes performing phantom validation experiments and translating our device into clinical work.
High dose rate brachytherapy is a common procedure used in the treatment of gynecological cancers to irradiate malignant tumors while sparing the surrounding healthy tissue. While treatment may be delivered using a variety of applicator types, a hybrid technique consisting of an intracavitary applicator and interstitial needles allows for highly localized placement of the radioactive sources. To ensure an accurate and precise procedure, identification of the applicator and needle tips is necessary. The use of three-dimensional (3D) transrectal ultrasound (TRUS) and transabdominal ultrasound (TAUS) imaging has been previously investigated for the visualization of the intracavitary applicators. However, due to image artifacts from the applicator, needle tip identification is severely restricted when using a single 3D US view. To overcome this limitation and improve treatment outcome, we propose the use of image fusion to combine TRUS and TAUS images for the complete visualization of the applicator, needle tips, and surrounding anatomy. In this proof-of-concept work, we use a multimodality anthropomorphic pelvic phantom to assess the feasibility of image fusion and needle visualization using a hybrid brachytherapy applicator. We found that fused 3D US images resulted in accurate visualization of the pertinent structures when compared with magnetic resonance images. The results of this study demonstrate the future potential of image fusion in gynecological brachytherapy applications to ensure high treatment quality and reduce radiation dose to surrounding healthy tissue. This work is currently being expanded to other applicator types and is being applied to patients in a clinical trial.
Brachytherapy is often used in gynecologic cancer treatment to provide high radiation doses to tumors and spare nearby healthy tissues. Intracavitary applicators, including tandem-and-ovoid and tandem-and-ring, are commonly used to position the radioactive sources appropriately. Three-dimensional (3D) transrectal ultrasound (TRUS) imaging has been demonstrated to allow for consistent delineation of the clinical target volume; however, the ability to visualize applicators and relevant structures following applicator insertion has not been investigated. We propose the use of a 3D TRUS system to visualize applicators at the time of placement. In two patient images, the key components of the tandem-and-ovoid applicators were clearly visualized, as well as the uterus, cervix, and vagina, with the potential to identify the tumor and organs-at-risk in these images. Although the tandem-and-ring applicator (one patient) obscured the cervix and anterior anatomy, the posterior applicator edges were visualized and we propose combining the 3D TRUS image with a 3D transabdominal ultrasound (TAUS) image for more complete visualization of the necessary structures. We designed a multimodality application-specific pelvic phantom to assess the feasibility of the image fusion and performed preliminary feasibility assessment on a tandem-and-ovoids applicator and a tandem-and-ring applicator with an interstitial ring cap. The resulting phantom images showed promising features for future image fusion. Intraoperative assessment of applicator placement has the potential to improve the treatment quality and reduce the risk of complications from overexposure of nearby normal tissues, as well as provides a promising approach for accessible image-guided brachytherapy, facilitating broader adoption to healthcare cost-constrained settings.
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