Brachytherapy is an important component in the multi-modality definitive treatment for cervical cancer and other recurrent gynecologic cancers. Delivering a high dose to the tumor target and low dose to nearby organs at risk (OARs) is critical for improving disease control and minimizing toxicity. The American Brachytherapy Society (ABS) recommends high-dose-rate (HDR) brachytherapy and provides treatment guidelines. However, significant practice variation persists, reflecting differences in clinic workflows and resource availability across the United States and internationally [1,2].

Both the ABS and the American Society for Radiation Oncology (ASTRO) clinical practice guidelines recommend incorporating three-dimensional (3D) imaging into treatment planning to better delineate tumor extent and optimize target coverage and OAR dosimetry. Data suggest that image-guided brachytherapy is associated with improved oncologic outcomes and reduced toxicity [3,4]. However, barriers such as cost, skill, and workflow limitations often hinder widespread implementation [5]. Although volumetric treatment planning has led to improvements in dosimetry and clinical outcomes, the quality of brachytherapy applicator placement remains foundational. There is limited modern literature focusing on techniques to optimize implantation accuracy.

The geometric relationship between the brachytherapy applicator, the tumor, and the OARs ultimately determines the achievable plan quality [2,4,6]. While smaller tumors can be treated effectively with intracavitary or hybrid applicators, large or recurrent tumors frequently require an interstitial implant with numerous needles, introducing potential for significant variation in needle placement and toxicity given the procedure's invasiveness [4,7]. Implants may be performed under no image guidance or with tools such as fluoroscopy, ultrasound, or 3D imaging. There are few recent publications concerning the use of real-time imaging during implantation in the age of volumetric planning.

We investigated how the implementation of transrectal ultrasound (TRUS) as a replacement for fluoroscopy during interstitial applicator placement for gynecologic HDR brachytherapy impacted needle channel utilization, needle accuracy, and radiation plan dosimetry. We hypothesized that using TRUS would result in fewer needles placed, fewer needles requiring removal, fewer unused needle channels, sustained high-dose target coverage, and low dose to nearby OARs.