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.
KEYWORDS: 3D image processing, 3D acquisition, Computed tomography, Visualization, Tumors, Ultrasonography, Image visualization, 3D image reconstruction, High dynamic range imaging, Imaging systems
Brachytherapy, a type of radiotherapy, may be used to place radioactive sources into or in close proximity to tumors, providing a method for conformally escalating dose in the tumor and the local area surrounding the malignancy. High-dose-rate interstitial brachytherapy of vaginal tumors requires precise placement of multiple needles through holes in a plastic perineal template to deliver treatment while optimizing dose and avoiding overexposure of nearby organs at risk (OARs). Despite the importance of needle placement, image guidance for adaptive, intraoperative needle visualization, allowing misdirected needles to be identified and corrected during insertion, is not standard practice. We have developed a 360-deg three-dimensional (3-D) transvaginal ultrasound (TVUS) system using a conventional probe with a template-compatible custom sonolucent vaginal cylinder and propose its use for intraoperative needle guidance during interstitial gynecologic brachytherapy. We describe the 3-D TVUS mechanism and geometric validation, present mock phantom procedure results, and report on needle localization accuracy in patients. For the six patients imaged, landmark anatomical features and all needles were clearly visible. The implementation of 360-deg 3-D TVUS through a sonolucent vaginal cylinder provides a technique for visualizing needles and OARs intraoperatively during interstitial gynecologic brachytherapy, enabling implants to be assessed and providing the potential for image guidance.
During high-dose-rate (HDR) interstitial brachytherapy of gynecologic malignancies, precise placement of multiple needles is necessary to provide optimal dose to the tumor while avoiding overexposing nearby healthy organs, such as the bladder and rectum. Needles are currently placed based on preoperative imaging and clinical examination but there is currently no standard for intraoperative image guidance. We propose the use of a three-dimensional (3D) ultrasound (US) system incorporating three scanning geometries: 3D transrectal US (TRUS), 360° 3D sidefire transvaginal US (TVUS), and 3D endfire TVUS, to provide an accessible and versatile tool for intraoperative image guidance during interstitial gynecologic brachytherapy. Images are generated in 12 - 20 s by rotating a conventional two-dimensional US probe, providing a reconstructed 3D image immediately following acquisition. Studies of needles in patient images show mean differences in needle positions of 3.82 ± 1.86 mm and 2.36 ± 0.97 mm in TRUS and sidefire TVUS, respectively, when compared to the clinical x-ray computed tomography (CT) images. A proof-of-concept phantom study of the endfire TVUS mode demonstrated a mean positional difference of 1.91 ± 0.24 mm. Additionally, an automatic needle segmentation tool was tested on a 360° 3D TVUS patient image resulting in a mean angular difference of 0.44 ± 0.19 ° and mean positional difference of 0.78 ± 0.17 mm when compared to manually segmented needles. The implementation of 3D US image guidance during HDR interstitial gynecologic brachytherapy provides a versatile intraoperative system with the potential for improved implant quality and reduced risk to nearby organs.
In high-dose-rate (HDR) interstitial gynecologic brachytherapy, needles are positioned into the tumor and surrounding area through a template to deliver radiotherapy. Optimal dose and avoidance of nearby organs requires precise needle placement; however, there is currently no standard method for intra-operative needle visualization or guidance. We have developed and validated a 360° three-dimensional (3D) transvaginal ultrasound (TVUS) system and created a sonolucent vaginal cylinder that is compatible with the current template to accommodate a conventional side-fire ultrasound probe. This probe is rotated inside the hollow sonolucent cylinder to generate a 3D image. We propose the use of this device for intra-operative verification of brachytherapy needle locations. In a feasibility study, the first ever 360° 3D TVUS image of a gynecologic brachytherapy patient was acquired and the image allowed key features, including bladder, rectum, vaginal wall, and bowel, to be visualized with needles clearly identifiable. Three patients were then imaged following needle insertion (28 needles total) and positions of the needles in the 3D TVUS image were compared to the clinical x-ray computed tomography (CT) image, yielding a mean trajectory difference of 1.67 ± 0.75°. The first and last visible points on each needle were selected in each modality and compared; the point pair with the larger distance was selected as the maximum difference in needle position with a mean maximum difference of 2.33 ± 0.78 mm. This study demonstrates that 360° 3D TVUS may be a feasible approach for intra-operative needle localization during HDR interstitial brachytherapy of gynecologic malignancies.
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