Image Localization For Frameless Stereotactic Radiotherapy

James Metz, MD
OncoLink Associate Editor
Last Modified: November 2, 1999

Presenter: Sanford L. Meeks, MD
Affiliation: University of Iowa

Summary:
Confirmation of accurate patient positioning is paramount in treatment of tumors utilizing stereotactic radiotherapy. Typically, invasive head rings are used for the treatment of many patients with CNS disease. The University of Florida has utilized infrared emitting diodes since 1995 for localization with stereotactic radiotherapy. This presentation evaluates the feasibility of utilizing a system that does not require an invasive head frame. This system utilizes optical guidance for stereotactic radiotherapy with infrared emitting diodes to determing the position of the patient in relation to the accelerator.

Methods:

A maxillary dental fixation device that contains imbedded infrared light emitting diodes is utilized
Aluminum fiducial markers are also imbedded in the device so position can be registered on a CT scanner
A CCD camera array detects the diodes and is interfaced to a computer
The dental fixation device is digitally localized in the treatment room
Results:
- The average accuracy of isocenter localization is 0.34 mm +/- 0.13 mm
- When the system utilizing an invasive headframe is compared to standard localization techniques, the difference is 0.65 mm +/- 0.17 mm
- Frameless localization agrees to conventional stereotactic localization to an average accuracy of 1.1 mm
Clinical/Scientific Implications:
- The authors are now evaluating this system of localization for frameless stereotactic radiotherapy utilizing passive markers
- It is currently recommended that a 2 mm margin is utilized to account for localization uncertainty
- Reproducable and accurate localization with less invasive procedures such as this should be further evaluated
ASTRO coverage is sponsored, in part, by Varian Medical Systems, Inc.