MR-Tracked Deflectable Stylet for Gynecologic Brachytherapy

Brachytherapy is a radiation based treatment that is implemented by precisely placing focused radiation sources into tumors. In advanced interstitial cervical cancer bracytherapy treatment, this is performed by placing a metallic rod (“stylet”) inside a hollow cylindrical tube (“catheter”) and advancing the pair to the desired target. The stylet is removed once the target is reached, followed by the insertion of radiation sources into the catheter. However, manually advancing an initially straight stylet into the tumor with millimeter spatial accuracy has been a long-standing challenge, which requires multiple insertions and retractions, due to the unforeseen stylet deflection caused by the stiff muscle tissue that is traversed. In this article, we develop a novel tendon-actuated deflectable stylet equipped with MR active-tracking coils that may enhance brachytherapy treatment outcomes by allowing accurate stylet trajectory control. In this article, we present the design concept and fabrication method, followed by the kinematic and mechanics models of the deflectable stylet. The hardware and theoretical models are extensively validated via benchtop and magnetic resonance imaging (MRI)-guided characterization. At insertion depths of 60 mm, benchtop phantom targeting tests provided a targeting error of
$1.23 \pm 0.47$
mm, and porcine tissue targeting tests provided a targeting error of
$1.65 \pm 0.64$
mm, after only a single insertion. MR-guided experiments indicate that the stylet can be safely and accurately located within the MRI environment.