Effect of fiducial marker defects on stereotactic target localization in the Leksell stereotactic system

The stereotactic procedure in neurosurgery is a minimally invasive technique used to treat intracranial lesions. The fiducial markers of a frame-based stereotactic procedure are important for defining the stereotactic coordinate system and in locating the target. These markers are often defective in stereotactic images owing to the presence of air bubbles in the imaging indicator. We have assessed the effect of these defects on the registration of an image and on the localization of a target. The virtual phantom method was employed to simulate various types of defect. The virtual images were registered using the Leksell GammaPlan® (LGP) radiosurgery planning system, and the image definition and the target localization errors were assessed. As a result, the effect of the defects was most severe when the majority of the marker disappeared, but not all, especially in the posterior region. The mean and maximum image definition errors were 0.1 and 1.4 mm, which caused the mean target localization error to be 0.2 and 0.0 mm in LGP version 5.34 and 8.3.1, respectively. It is recommended to exclude images with defective fiducial markers during the image definition procedure to minimize subsequent errors, though the newest version of LGP (version 8.3.1) corrects localization errors.