TH‐C‐220‐09: High Resolution Image‐Guided Irradiation of Murine Brain Tumors Using the Gamma Knife Perfexion Treatment Unit

Abstract

Purpose: To provide a method of accurate, submillimeter image‐guidance for the targeting of small brain tumors in an array of 5 mice when irradiating with the Gamma Knife Perfexion treatment unit. Small‐animal models provide a useful platform for studying the effects of radioprotectors and radiosensitizers on normal brain tissue and tumors. Efficient irradiation of an array of up to 5 mice in a single programmed sequence, using the Leksell Gamma Knife Perfexion (GKPfx) treatment unit, is an ongoing technique at our institution. One challenge in the process is to accurately guide the 4‐ mm‐diameter radiation beamsˈ focus of the GKPfx treatment unit to irradiate only a small region of interest (ROI) that includes the hippocampus. This can be accomplished through image guidance using a high‐field, high‐resolution small‐animal MR imager and transforming the ROI image coordinates to Leksell stereotactic treatment coordinates. Materials and Methods: Uniquely‐tagged mice were individually‐scanned using a small‐animal MR imager. Prior to scanning, each mouse was carefully positioned and immobilized with ear bars and a bite bar using a specially designed mouse holder module, which has three, CT‐ and MR‐ viewable, fiducials embedded within it. The fiducials provide a 3‐D frame of reference to transform ROI image coordinates to Leksell stereotactic coordinates. A Matlab script displays the image set, provides a tool to locate fiducials and other ROIs in image coordinates, computes the coordinate system transforms and saves results in an Excel worksheet. Transform computation uses Hornˈs quaternion‐based method. Results: The previously described method shows accuracy of less than 1.0 mm, when imaging resolution is 0.3 mm in X and Y and 1.0mm in Z. Computation for one mouse holder position takes less than 2 s on 1.8GHz Centrino Duo PC.Conclusions: This image‐guided technique provides for fast and accurate MR/CT localized radiation targeting of mouse brain.