Evaluation of Image-Guided Positioning for Frameless Intracranial Radiosurgery
Received 29 August 2008; received in revised form 9 December 2008; accepted 8 January 2009. published online 27 March 2009.
Purpose
The standard for target alignment and immobilization in intracranial radiosurgery is frame-based alignment and rigid immobilization using a stereotactic head ring. Recent improvements in image-guidance systems have introduced the possibility of image-guided radiosurgery with nonrigid immobilization. We present data on the alignment accuracy and patient stability of a frameless image-guided system.
Methods and Materials
Isocenter alignment errors were measured for in vitro studies in an anthropomorphic phantom for both frame-based stereotactic and frameless image-guided alignment. Subsequently, in vivo studies assessed differences between frame-based and image-guided alignment in patients who underwent frame-based intracranial radiosurgery. Finally, intratreatment target stability was determined by image-guided alignment performed before and after image-guided mask immobilized radiosurgery.
Results
In vitro hidden target localization errors were comparable for the framed (0.7 ± 0.5 mm) and image-guided (0.6 ± 0.2 mm) techniques. The in vivo differences in alignment were 0.9 ± 0.5 mm (anteroposterior), −0.2 ± 0.4 mm (superoinferior), and 0.3 ± 0.5 mm (lateral). For in vivo stability tests, the mean distance differed between the pre- and post-treatment positions with mask-immobilized radiosurgery by 0.5 ± 0.3 mm.
Conclusion
Frame-based and image-guided alignment accuracy in vitro was comparable for the system tested. In vivo tests showed a consistent trend in the difference of alignment in the anteroposterior direction, possibly due to torque to the ring and mounting system with frame-based localization. The mask system as used appeared adequate for patient immobilization.
∗Department of Radiation Oncology, Brain Tumor Center, University of Cincinnati Neuroscience Institute, University of Cincinnati College of Medicine, Cincinnati, OH
†Department of Neurosurgery, Brain Tumor Center, University of Cincinnati Neuroscience Institute, University of Cincinnati College of Medicine, Cincinnati, OH
Reprint requests to; Michael Lamba, Ph.D., Division of Radiation Oncology, University of Cincinnati College of Medicine, 234 Goodman St., ML0757, Cincinnati OH 45267-0757. Tel: (513) 584-9028; Fax: (513) 584-4007
Conflict of interest: The authors have received funds (<$10,000) from BrainLAB as a nonrestricted educational grant.
ABSTRACT