Purpose: to evaluate the utilization of endovascular fiducial markers for real-time image registration and tracking in CyberKnife (CK) (Accuray, Sunnyvale, CA) radiotherapy. Patients at high risk of complications from percutaneous transthoracic fiducial insertion may benefit from an endovascular approach using embolization microcoils.
Methods: Three sizes (8x8mm, 2x5mm, 2x3mm) of Platinum Tornado Embolization Microcoils (Cook Inc, Bloomington, IN) were tested for functionality as fiducial markers with the CK real-time tracking system. The detectability of the fiducials on the CK imaging system was first evaluated based on the fiducial tracking algorithm parameters. The 2x3mm microcoil was inserted into a Respiratory Motion Phantom (Modus Medical Devices, Ontario, CAN) to be tested with the institution’s 4DCT motion assessment process. To evaluate the microcoil targeting accuracy for planning and treatments, a Synchrony tracking end-to-end (E2E) test was performed, and the total targeting error calculated as the offset between measured and planned 70% isodose lines. Lastly, the patient-specific QA of a clinical lung case was delivered to a MapCheck2 device (Sun Nuclear Corporation, Melbourne, FL), using the microcoils as tracking markers, and resulting dose distribution evaluated using the gamma index analysis with 2%/2mm and 10% dose threshold criteria.
Results: Following initial detectability tests, the 2x3mm coil produced fiducial tracking algorithm parameters within manufacturer-recommended tolerances during real-time alignment and is appropriate for clinical use. The lung phantom motion assessment with the microcoils on the 4DCT scan matched the expected breathing motion within 1mm. The total targeting error of the Synchrony E2E test was 0.99mm, which is within the 1.5mm tolerance recommended by AAPM Task Group 135. The patient-specific QA of the clinical lung SBRT plan resulted in a 100% passing rate.
Conclusion: The 2x3mm Platinum Tornado Embolization Microcoil performance is satisfactory as a marker for real-time CK tracking and can be employed for CK treatments.
Not Applicable / None Entered.