Toward three-dimensional ultrasound image fusion for the guidance of gynecological brachytherapy procedures

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.