How to Place Fiducials for Radiation Therapy

Traditional radiation therapy (RT), involving the delivery of high doses of toxic radiation to a target field, is wrought with the unfortunate consequence of acute and chronic injury to healthy tissue adjacent to the tumor. The development of real-time image-guided radiation therapy systems allows for the safe delivery of focal high-dose RT to target lesions while minimizing the amount of collateral damage to normal tissue. Traditional fiducials are cylindrical gold seeds measuring 3-5 mm in length by 0.75-1.2 mm in diameter, and are deployed using a 19-gauge fine needle aspiration needle. Given the ability of endoscopic ultrasound (EUS) to allow for close proximity to structures in the mediastinum, abdomen, and pelvis that may not otherwise be accessible by percutaneous approaches, the use of EUS-guided fiducial placement into both luminal and extraluminal targets has become an accepted technique.