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Evaluation of Target Dose Coverage with Real-Time Robotic Head Motion Stabilization in Single-Isocenter Multi-Target SRS: A Phantom Study

A Belcher

AH Belcher*, K Farrey , X Liu , RD Wiersma , The University of Chicago, Chicago, IL


SU-E-108-3 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 108

Purpose: Frameless maskless stereotactic radiosurgery (SRS) has the potential to improve upon the clinical workflow and patient comfort of frame-based SRS, but may increase dose coverage uncertainty due to a reduction in rigid immobilization. This can be particularly problematic in single-isocenter multi-target SRS, where head rotations may further degrade treatment efficacy due to a leveraging effect. Incorporating a novel robotic system for real-time head motion stabilization has the potential to improve target dose coverage. In this work, we examine the differences in treatment accuracy for several cases of head motion in a phantom for frameless maskless SRS.

Methods: A robot capable of performing highly precise 6DOF movements was developed, and a head phantom with 5 pieces of Gafchromic film placed within an internal cavity was fixed to the robotic system. An SRS treatment plan with 3 spherical targets was developed, and the phantom was treated under three conditions: with the robot performing previously-recorded head motion, the robot reproducing previously-recorded stabilized head motion from an earlier volunteer study, and a no-motion case. The film-recorded dose coverage for each case was then compared using Gamma analysis with 1% / 1mm distance-to-agreement criteria.

Results: Comparing the uncorrected head motion case and the stabilized motion case to the no-motion condition, the latter achieved a 95% pass rate in all but one slice, while the former only met this criterion at the central slice. Examining all slices, the stabilized case improved Gamma analysis agreement by 6.8% compared to the uncorrected motion case on average.

Conclusion: Target coverage was compared for three motion-based cases of single-isocenter multi-target SRS. Introduction of motion degrades target localization, but the use of simulated robotic head motion stabilization showed good agreement with the no-motion case, demonstrating the potential for real-time 6DOF robotic head stabilization to improve frameless maskless SRS treatment accuracy.

Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by the National Institutes of Health T32-EB002103 Training Grant from the National Institute of Biomedical Imaging and Bioengineering, and by American Cancer Society grant RSG-13-313-01-CCE.

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