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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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