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The OncoReach Stylet for Brachytherapy: Design Evaluation and Pilot Study

Pejman Kheradmand, Kent K. Yamamoto, Emma Webster, Keith Sowards, Gianna Hatheway, Katharine L. Jackson, Sabino Zani, Julie A. Raffi, Diandra N. Ayala-Peacock, Scott R. Silva, Joanna Deaton Bertram, Yash Chitalia

TL;DR

The study presents the OncoReach stylet, a tendon-driven steerable device integrated with standard interstitial brachytherapy needles to enable curved trajectories for cervical cancer treatment. A two-tube Cosserat rod model predicts device shape under tendon actuation, guiding design choices such as joint count and placement; the best-performing configuration (15G, 30 joints at the tip) balances bending compliance with axial stiffness. Experimental validation in free space confirms model accuracy, while a patient-derived uterus–pelvis phantom pilot demonstrates the ability to steer from medial entries to lateral targets, achieving curvatures that exceed typical directional errors in conventional needle placement. The work suggests steerable stylets can enhance targeting accuracy and potentially reduce needle counts in ISBT, with future work focusing on tissue-force modeling, real-time sensing, and broader clinical testing.

Abstract

Cervical cancer accounts for a significant portion of the global cancer burden among women. Interstitial brachytherapy (ISBT) is a standard procedure for treating cervical cancer; it involves placing a radioactive source through a straight hollow needle within or in close proximity to the tumor and surrounding tissue. However, the use of straight needles limits surgical planning to a linear needle path. We present the OncoReach stylet, a handheld, tendon-driven steerable stylet designed for compatibility with standard ISBT 15- and 13-gauge needles. Building upon our prior work, we evaluated design parameters like needle gauge, spherical joint count and spherical joint placement, including an asymmetric disk design to identify a configuration that maximizes bending compliance while retaining axial stiffness. Free space experiments quantified tip deflection across configurations, and a two-tube Cosserat rod model accurately predicted the centerline shape of the needle for most trials. The best performing configuration was integrated into a reusable handheld prototype that enables manual actuation. A patient-derived, multi-composite phantom model of the uterus and pelvis was developed to conduct a pilot study of the OncoReach steerable stylet with one expert user. Results showed the ability to steer from less-invasive, medial entry points to reach the lateral-most targets, underscoring the significance of steerable stylets.

The OncoReach Stylet for Brachytherapy: Design Evaluation and Pilot Study

TL;DR

The study presents the OncoReach stylet, a tendon-driven steerable device integrated with standard interstitial brachytherapy needles to enable curved trajectories for cervical cancer treatment. A two-tube Cosserat rod model predicts device shape under tendon actuation, guiding design choices such as joint count and placement; the best-performing configuration (15G, 30 joints at the tip) balances bending compliance with axial stiffness. Experimental validation in free space confirms model accuracy, while a patient-derived uterus–pelvis phantom pilot demonstrates the ability to steer from medial entries to lateral targets, achieving curvatures that exceed typical directional errors in conventional needle placement. The work suggests steerable stylets can enhance targeting accuracy and potentially reduce needle counts in ISBT, with future work focusing on tissue-force modeling, real-time sensing, and broader clinical testing.

Abstract

Cervical cancer accounts for a significant portion of the global cancer burden among women. Interstitial brachytherapy (ISBT) is a standard procedure for treating cervical cancer; it involves placing a radioactive source through a straight hollow needle within or in close proximity to the tumor and surrounding tissue. However, the use of straight needles limits surgical planning to a linear needle path. We present the OncoReach stylet, a handheld, tendon-driven steerable stylet designed for compatibility with standard ISBT 15- and 13-gauge needles. Building upon our prior work, we evaluated design parameters like needle gauge, spherical joint count and spherical joint placement, including an asymmetric disk design to identify a configuration that maximizes bending compliance while retaining axial stiffness. Free space experiments quantified tip deflection across configurations, and a two-tube Cosserat rod model accurately predicted the centerline shape of the needle for most trials. The best performing configuration was integrated into a reusable handheld prototype that enables manual actuation. A patient-derived, multi-composite phantom model of the uterus and pelvis was developed to conduct a pilot study of the OncoReach steerable stylet with one expert user. Results showed the ability to steer from less-invasive, medial entry points to reach the lateral-most targets, underscoring the significance of steerable stylets.
Paper Structure (17 sections, 12 equations, 4 figures)

This paper contains 17 sections, 12 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Design
  3. Front-end and Back-end Design
  4. Handheld Prototype Design
  5. Mechanical Model
  6. Static Model
  7. Uterus-Pelvis Phantom Model
  8. Uterus Phantom Model
  9. Pelvis Phantom Model
  10. Pelvic Tissue Phantom Model
  11. Model Formation and Assembly
  12. Experiments and Results
  13. Free-Space Experimental Setup
  14. Mechanical Model Validation
  15. OncoReach Pilot Study
  16. ...and 2 more sections

Figures (4)

  • Figure 1: Comparison between the model-predicted centerline (red) and experimental ground-truth data (black markers) for various configurations of the stylet and needle. (a-c) depict 15-gauge needle-stylet assembly configurations with varying spherical joint counts. (d-e) present configurations with 20 spherical joints while varying placement from the base to the midsection of the stylet.
  • Figure 2: Pilot study setup: phantom with Syed template and tandem attached. (a) Expert user using the ultrasound probe to visualize tandem inside uterus. (b) Tandem entering the Humimic gel inside the uterus. (c) Obturator fitting inside the vaginal cavity. (d) Pilot study setup.
  • Figure 3: Needle insertion results. (a) Inferior view of the phantom, highlighting entry points and their respective CT sub-figures (target location - straight/steered): (b) Anterior-Straight, (c) Anterior-Steered, (d) Medial-Straight, (e) Medial-Steered, (f) Posterior-Straight, (g) Posterior-Steered.
  • Figure 4: OncoReach Pilot Study Results