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Program Information

Multi-Catheter Rotating Shield Brachytherapy Control System

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K Patwardhan

R Flynn1 , Y Kim1 , X Wu2 , W Xu2 , H Dadkhah2 , M Cho2 , K Patwardhan1*, (1) University of Iowa Hospitals and Clinics, Iowa City, IA, (2) University of Iowa, Iowa City, IA.


WE-AB-605-8 (Wednesday, August 2, 2017) 7:30 AM - 9:30 AM Room: 605

Purpose: To introduce a novel control system for the angular positioning of multiple partially-shielded Gd-153 sources in an interstitial Rotating Shield Brachytherapy (RSBT) system for prostate cancer. The RSBT system enables a reduction of urethral dose by up to 40% relative to conventional high-dose-rate brachytherapy. The control system has a ±3° angular positioning accuracy requirement, resulting in a ±3% dosimetric accuracy in the prostate, bladder, rectum, and urethra.

Methods: Catheter rotation angles are controlled by a moving template that causes rotational motion of all catheters as it translates between two stationary templates. The control system has ten auto-focus (35mm-infinity), 2592 x 1944 pixel resolution cameras (∅14mm x 26mm) that measure the angular catheter positions in real time. Cameras are optimally oriented to provide maximum viewing redundancy. Catheter angles are determined using canny edge detection based pattern recognition algorithm that detects angle-dependent etchings on the catheter walls. Angles of obscured catheters are estimated based on those of visible catheters using a co-variance table. Variation in the catheter angles are managed by optimizing the moving template position and orientation such that the sum of all angular uncertainties of the catheters is minimized. A prototype angle control system was constructed for validation.

Results: A nine-catheter RSBT system was simulated. Deviations were introduced in the initial catheter positions and the orientation of the moving template to test the effectiveness of the control system. Angular uncertainties when using the control system were found to be within ±1.5° of the desired treatment position using optimization and feedback compared to ±7°-10° without it. The achievable angular accuracy of ±1.5° was confirmed using the prototype system.

Conclusion: The proposed catheter angle control system enables the RSBT delivery accuracy to be kept within ±3%.

Funding Support, Disclosures, and Conflict of Interest: This work was funded by NIH R01 EB020665 and NIH 1R41 CA210737-01. Ryan Flynn has financial interest in pxAlpha, LLC, which is developing a Rotating Shield Brachytherapy product.

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