ACCURACY OF AN EXPERIMENTAL STEREOTAXIC SYSTEM FOR MRI-BASED GAMMA-KNIFE IRRADIATION IN THE RAT

Stereotactic devices for experimental Gamma Knife irradiation and magn etic resonance imaging (MRI) have recently been developed for experime ntal studies using rats [6, 7]. The present study examined the accurac y of these devices using the following two approaches. In the first ap proach, Gamma Knife irradiation was performed using the stereotactic d evice with targets based on a standard stereotactic atlas. Gadolinium- enhanced T1-weighted magnetic resonance imaging was performed using th e MRI stereotactic device. Animals were then sacrificed after Evans bl ue injection. and the rat brain was sliced using an attachment to the stereotactic device. The center coordinates of the gadolinium-enhanced area from the MRI and Evans blue-stained area from the tissue section s were obtained using a computer-assisted image analysis system. These coordinates were compared with the target coordinates planned from th e stereotactic atlas. In the second approach, a thermoluminescence dos imeter was implanted in the rat brain. Stereotactic MRI was performed using the stereotactic MRI device, and the coordinates of the implant were obtained. Gamma Knife irradiation was then performed at this targ et using the stereotactic device. The absorbed dose was measured and c ompared with the planning dose. These experiments demonstrated a spati al error of 0.6 mm (standard error +/- 0.07) between Gamma Knife irrad iation based on a comparison of the atlas coordinates and the lesion, and a spatial error of 1.0 mm (standard error +/- 0.13) based on a com parison of the stereotactic MR images and the lesion. Gamma Knife irra diation based on MR images using the stereotactic device demonstrated a maximum error of 10% in absorbed dose at the target center. Together , the stereotactic devices for Gamma Knife irradiation and magnetic re sonance imaging provide useful tools for Gamma Knife research in an an imal model.