# Approaches to needle navigation in interstitial brachytherapy using infrared tracking and radiography

## TL;DR

This paper introduces two methods for guiding brachytherapy needles using infrared tracking and x-ray imaging to reduce the need for multiple CT scans during treatment.

## Contribution

The novel contribution is combining infrared tracking with planar x-ray imaging for real-time needle path reconstruction and correction.

## Key findings

- Using two x-ray images with a 20° offset, the needle path was reconstructed with less than 1 mm deviation from CT scans.
- A single x-ray image approach with prior bending data achieved tip deviations below 1.3 mm.
- Both methods were validated in preclinical studies and showed potential to improve clinical workflows.

## Abstract

Intraoperative cone‐beam computed tomography (CBCT) provides a valuable option for accurate three‐dimensional applicator positioning in gynecologic brachytherapy, but is associated with radiation exposure and increased intervention time especially in case of repeated CBCT imaging being required for creating a sufficient implant arrangement.

To reduce the need for multiple CBCT scans for corresponding applicator verification, this work proposes two methods for needle path navigation, including corrections of potential bending in situ, by combining infrared tracking with planar x‐ray imaging for enabling accurate intraoperative needle guidance.

An examined 200 mm brachytherapy needle was rigidly mounted on an infrared‐reflective tracking tool to enable real time tracking. Two planar x‐ray images, acquired from varying distinct angles, were used to determine the exact 3D position of the needle tip region via backprojection. A spline was fitted through the obtained coordinates to reconstruct the full needle path. Based on this, only a single initial CBCT scan was required to visualize the predicted needle path within this scan. Additionally, a second approach for needle prediction was presented focusing on only one planar x‐ray image by incorporating prior needle bending information from the initial CBCT scan. Both methods were evaluated in preclinical studies and validated against a corresponding ground‐truth obtained from CBCT.

The proposed method considering two planar x‐ray images successfully reconstructed the needle path with deviations of less than 1 mm from the CBCT reference scan, when using at least 20° offset between the x‐ray image acquisitions. The single‐scan approach, using prior bending information, yielded promising results with deviations at the tip of below 1.3 mm.

Both described methods demonstrated their feasibility in preclinical studies, showing potential to improve and accelerate clinical implantation workflows by means of needle navigation in the future.