SU‐FF‐T‐548: Comparison of Cone‐Beam CT and Frame‐Based Localizations for Stereotactic Radiosurgery with Fixed Head Rings and Removable Frames
Objectives: To compare localization accuracy using both conventional frame‐based localizers and cone‐beam CT (CBCT) images for stereotactic radiosurgery (SRS). Methods: A SRS geometric phantom was used to verify the localization accuracy based on a SRS localizer (BrainLAB) and CBCT images (NovalisTx, Varian Medical Systems). 70 patients with 86 SRS treatments were retrospectively analyzed (11 with fixed head rings and 75 with removable U‐Frames with additional skin masks). Patients were localized with the Brainlab localizer first. CBCT images with 1 mm slice thickness were then acquired to match planning CT. Results: The SRS geometric phantom showed that the Brainlab localizer and CBCT images based localizations agreed within 1 mm. The magnitudes of shifts between the Brainlab localizer and CBCT images based localizations for SRS with fixed head rings were 0.04 ± 0.05 cm along x (lateral), 0.09 ± 0.06 cm along y (vertical), and 0.08 ± 0.08 cm along z (longitudinal) direction with 0.06 ± 0.14 degrees of couch rotation. For the SRS patients using removable U‐frames with masks, the magnitudes of shifts between the Brainlab localizer and CBCT images based localizations were 0.11 ± 0.10 cm along x, 0.12 ± 0.09 cm along y, and 0.18 ± 0.13 cm along z direction with 0.34 ± 0.53 degrees of couch rotation. The 95% probability shifts for the removable frame were 0.3 cm along x, 0.3 cm along y, and 0.4 cm along z direction with 1.6 degrees of couch rotation. Conclusions: The results from both the phantom test and the patients with a fixed head ring show that the CBCT based localization is reliable and accurate. For patients with removable frames, if the localization is based only on the frame‐based localizer without any imaging guidance, a margin of 3 ∼ 4 mm is necessary to ensure adequate coverage. © 2009, American Association of Physicists in Medicine. All rights reserved.
Wang, Z; Kirkpatrick, J; Wu, Q; Chang, Z; Willett, C; Yin, F
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