The Synchrony® (Accuray Incorporated, Sunnyvale, CA) Respiratory Tracking System allows the CyberKnife®(Accuray Incorporated, Sunnyvale, CA) to deliver precisely high-dose radiation to targets that move with respiration. Tracking of moving tumors currently requires the use of implanted radiographic markers (or fiducials) as reference points [1, 7]. Several reports describe the placement of fiducials through surgical or percutaneous methods under image guidance (ultrasonography or computed tomography) in the prostate, spine, and lungs [2, 3, 6-8]. Fiducial implantation surgery can be invasive, and the percutaneous approach carries risks and limitations, especially when the lesions are in a deep location such as the posterior mediastinum or the abdomen. Innovations in the fiducial implantation procedure may improve its accuracy and reduce its risks, ultimately enhancing comfort for the patient. We recently described a new approach to placing fiducials in these deep structures using endoscopic ultrasound (EUS) .
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