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PURPOSE: Early stage breast cancer is typically treated with lumpectomy. During lumpectomy, electromagnetic tracking can be used to monitor tumor position using a localization needle with an electromagnetic sensor fixed on the needle shaft. This needle is stabilized in the tumor with tissue locking wire hooks, which are deployed once the needle is inserted. The localization needle may displace from its initial position of insertion due to mechanical forces, providing false spatial information about the tumor position and increasing the probability of an incomplete resection. This study investigates whether gravitational and mechanical forces affected the magnitude of needle displacement. METHODS: Ten ultrasound scans were evaluated to measure needle displacement in vivo. Needle position was approximated by the distance between the needle tip and the tumor boundary on a 2D ultrasound image, and needle displacement was defined by the change in position. The angle between the localization needle and the coronal plane was computed in an open-source platform. RESULTS: A significant relationship (p = 0.04) was found between the needle to coronal plane angle and increased needle displacement. Needles inserted vertically, pointing towards the operating room ceiling, tended to exhibit greater needle displacement. Average needle displacement was 1.7 ±1.2 mm. CONCLUSION: Angle between the needle and the horizontal plane has been shown to affect needle displacement, and should be taken into consideration when inserting the localization needle. Future works can be directed towards improving the clinical workflow and mechanical design of the localization needle to reduce slippage during surgery.
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