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Mechanical Evaluation of a Helical Drive System for Rotating Shield Brachytherapy in Prostate Cancer

Q Adams1*, K Hopfensperger2, Y Kim3, R Flynn4, (1) Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, (2) Department of Biomedical Engineering, The University of Iowa, Iowa City, IA, (3) Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, (4) Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To mechanically assess the potential clinical viability of a helical delivery system to enable rotating shield brachytherapy for prostate cancer based on the 169Yb isotope. Treatment delivery occurs in an automated manner using a single partially shielded source that treats each implanted needle in serial.

Methods: Helical source motion is generated by coupling the rotational and translational motion of a threaded rotating catheter which is connected to a nitinol needle containing the partially shielded source at its distal end. The catheter is controlled by a gear drive system containing a central gear with an asymmetric inner profile that corresponds to the axial profile of the catheter along its longitudinal axis. Precise control of the angular velocity of the threaded catheter enables the dose modulation. The threaded rotating catheter has a pitch of 5 mm to allow for up to 72 angular dwell positions per rotation. Rotational motion is generated by two sets of redundant high-torque, high-resolution stepper motors with angular precision of 0.9° per step controlled by a Duet 3 Mainboard 6HC. The prototype system was constructed using primarily 3-D printing and mechanical accuracy measurements of the helical source motion were obtained.

Results: A prototype of the catheter angular drive system was successfully constructed and evaluated for mechanical accuracy. Measured versus predicted catheter positions were within dosimetrically-validated thresholds of less than 0.5 mm for translation and less than 6° for angular orientation of the threaded catheter, satisfying accuracy requirements.

Conclusion: The prototyped catheter angular drive system was able to control helical motion of the source to within clinically relevant tolerances, demonstrating adequate mechanical accuracy. Successful production and evaluation of the prototyped system, which is a core component of a complete future clinical delivery system, provides initial evidence for the feasibility of RSBT clinical implementation for prostate cancer.

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Funding Support, Disclosures, and Conflict of Interest: RTF is the founder of pxAlpha, LLC, which is developing rotating shield brachytherapy technology.

Keywords

HDR, Brachytherapy, Radiation Therapy

Taxonomy

TH- Brachytherapy: Development (new technology and techniques)

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