Touching the tumor boundary: A pilot study on ultrasound based virtual fixtures for breast-conserving surgery

TL;DR

This study addresses the challenge of accurately delineating mobile, non-palpable breast tumor boundaries during breast-conserving surgery by introducing a cooperative robotic guidance system that uses haptic feedback to enforce virtual boundary constraints. The approach combines ultrasound and electromagnetic navigation with a small haptic device, implementing forbidden-region virtual fixtures to guide resection and prevent boundary breaches. In a pilot with breast simulants, the system reduced positive margins and decreased cognitive workload (as measured by NASA TLX), but increased resection time due to enhanced boundary palpation, highlighting a trade-off between accuracy and speed and the need for training and design optimization. The work contributes an open-source VF guidance framework, a method for real-time haptic constraint application, and initial evidence supporting the potential value of haptic guidance in improving breast-conserving surgery outcomes, with plans for broader validation and platform enhancements.

Abstract

Purpose: Delineating tumor boundaries during breast-conserving surgery is challenging as tumors are often highly mobile, non-palpable, and have irregularly shaped borders. To address these challenges, we introduce a cooperative robotic guidance system that applies haptic feedback for tumor localization. In this pilot study, we aim to assess if and how this system can be successfully integrated into breast cancer care. Methods: A small haptic robot is retrofitted with an electrocautery blade to operate as a cooperatively controlled surgical tool. Ultrasound and electromagnetic navigation are used to identify the tumor boundaries and position. A forbidden region virtual fixture is imposed when the surgical tool collides with the tumor boundary. We conducted a study where users were asked to resect tumors from breast simulants both with and without the haptic guidance. We then assess the results of these simulated resections both qualitatively and quantitatively. Results: Virtual fixture guidance is shown to improve resection margins. On average, users find the task to be less mentally demanding, frustrating, and effort intensive when haptic feedback is available. We also discovered some unanticipated impacts on surgical workflow that will guide design adjustments and training protocol moving forward. Conclusion: Our results suggest that virtual fixtures can help localize tumor boundaries in simulated breast-conserving surgery. Future work will include an extensive user study to further validate these results and fine-tune our guidance system.

Figures (6)

• Figure 1: Left: Close-up of resection tool which is the stylus of the Touch modified to hold a dull electrocautery blade. Right: The entire system, including the EM field generator, tracked needle, tracked utlrasound probe, reference sensor, and breast simulant.
• Figure 2: Software and hardware integration. In the top left legend the symbols associated with transformations that are sent between each program are also defined. Cautery in this diagram refers to the modified robotic resection tool.
• Figure 3: From left to right: Visual of the ultrasound motion during contouring. An example of the tumor contour on an ultrasound slice and the experimental set up with the robot and navigation interface on a laptop. Navigation views provided to the surgeon, frontal and sagittal view respectively.
• Figure 4: Left: User performing experiment with VF guidance system. Navigation interface is shown when the tip of the resection tool is outside of the tumor. Right: Navigation interface is shown when the the tip of the resection tool is in contact with the tumor.
• Figure 5: Left to right:Final resection, third round, from each independent user. The top row for each user is resections without VF guidance and bottom row is resection with VF guidance. For each user, the images in the left block show the resected specimen and the images in the right block show the complimentary resection cavity in the simulant. Blue in the resection cavity on the right indicates the presence of a positive margin. Top to bottom: Results from users 1-3, results from users 4-6.