Reducing set-up uncertainty in the Elekta Stereotactic Body Frame using Stealthstation software

The Elekta Stereotactic Body Frame (SBF) is a device which allows extracranial targets to be localized and irradiated in a stereotactic coordinate system. Errors of positioning of the body relative to the frame are indirectly estimated by image fusion of multiple CT scans. A novel repositioning methodology, based on neurosurgical Stealth technology, is presented whereby accurate patient repositioning is directly confirmed before treatment delivery. Repositioning was performed on four extracranial stereotactic radiosurgery patients and a radiotherapy simulation phantom. The setup error was quantitatively measured by fiducial localization. A confirmatory CT scan was performed and the resulting image set registered to the initial scan to quantify shifts in the GTV isocenter. Alignment confirmation using Stealth took between 5 and 10 minutes. For the phantom studies, a reproducibly of 0.6 mm accuracy of phantom-to-SBF alignment was measured. The results on four actual patients showed setup errors of 1.5 mm or less. Using the Stealth Station process, rapid confirmation of alignment on the treatment table is possible.