Evaluation of the Visibility and Artifacts of 11 Common Fiducial Markers for Image Guided Stereotactic Body Radiation Therapy in the Abdomen

Purpose: The purpose of this study was to quantitatively evaluate the visibility and artifacts of commercially available fiducial markers to optimize their selection for image guided stereotactic body radiation therapy. Methods and Materials: From 6 different vendors, we selected 11 fiducials commonly used in image guided radiation therapy. The fiducials varied in material composition (e.g., gold, platinum, carbon), shape (e.g., cylindrical, notched/linear, coiled, ball-like, step), and size measured in terms of diameter (0.28-1.0 mm) and length (3.0-20.0 mm). Each fiducial was centered in 4-mm bolus within a 13-cm-thick water-equivalent phantom. Fiducials were imaged with the use of a simulation computed tomography (CT) scanner, a CT-on-rails system, and an onboard cone beam CT system. Acquisition parameters were set according to clinical protocols. Visibility was assessed in terms of contrast (Δ Hounsfield unit [HU]) and the Michelson visibility metric. Artifacts were quantified in terms of relative standard deviation and relative streak artifacts level (rSAL). Twelve radiation oncologists ranked each fiducial in terms of clinical usefulness. Results: Contrast and artifacts increased with fiducial size. For CT imaging, maximum contrast (2722 HU) and artifacts (rSAL = 2.69) occurred for the largest-diameter (0.75 mm) platinum fiducial. Minimum contrast (551 HU) and reduced artifacts (rSAL = 0.65) were observed for the smallest-diameter (0.28 mm) gold fiducial. Carbon produced the least severe artifacts (rSAL = 0.29). The survey indicated that physicians preferred gold fiducials with a 0.35- to 0.43-mm diameter, 5- to 10-mm length, and coiled or cylindrical shape that balanced contrast and artifacts. Conclusions: We evaluated 11 different fiducials in terms of visibility and artifacts. The results of this study may assist radiation oncologists who seek to maximize contrast, minimize artifacts, or balance contrast versus artifacts by fiducial selection.