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Feasibility Study of Surgical Clips for Fiducial Tracking in CyberKnife System

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H Lee

H Lee*, J Yoon , E Lee , S Cho , K Park , W Choi , J Baek , K Keum , W Koom , Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea


SU-E-J-64 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To investigate the ability of CyberKnife to track surgical clips used as fiducial markers

Methods: The Octavius 1000SRS detector and solid water (RW3) slab phantom were used with motion platform to evaluate the study. The RW3 slab phantom was set up to measure the dose distribution from coronal plane. It consists of 9 plates and the thickness of each plate is 10mm. Among them, one plate was attached with 3 surgical clips, which are orthogonally positioned on outer region of array. The length of attached clip was represented as 1cm on planning CT. The clip plate was placed on the 1000SRS detector and 3 slabs were stacked up on the plate to build the measuring depth. Below the detector, 5 slabs were set. The two-axis motion platform was programmed with 1D sinusoidal movement (20mm peak-to-peak, 3s period) toward superior/inferior and left/right directions to simulate target motion. During delivery, two clips were extracted by two X-ray imagers, which led to translational error correction only. Synchrony was also used for dynamic tracking. After the irradiation, the measured dose distribution of coronal plane was compared with the planar dose distribution calculated by the CyberKnife treatment planning system (Multiplan) for cross verification. The results were assessed by comparing the absolute Gamma (γ) index.

Results: The dose distributions measured by the 1000SRS detector were in good agreements with those calculated by Multiplan. In the dosimetric comparison using γ-function criteria based on the distance-to-agreement of 3mm and the local dose difference of 3%, the passing rate with γ-parameter ≤1 was 91% in coronal plane.

Conclusion: The surgical clips can be considered as new fiducials for robotic radiosurgery delivery by considering the target margin with less than 5mm.

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