DESCRIPTION OF A STEREOTAXIC DEVICE FOR E XPERIMENTAL GAMMA-KNIFE RADIOSURGERY IN RATS

To allow the experimental use in rats of a Gamma Knife Radiosurgical U nit, a stereotactic device adapted from the conventional Kopf's device was developed. To control the accuracy of the coordinate system based on the De Groot's rat stereotactic atlas, experimental radiosurgical lesions were made on the left striatum. The isodose curve distribution of the 4 mm collimator was calculated with the dose planning software used in Gamma Knife and superimposed on the left striatum target. Dos es of 200 Gy were administred to the left striatum in six rats. The re sults were evaluated 21, 34 and 47 days later. At 34 and 47 days necro tic lesions were exactly as targeted. In a second group of 48 rats rec eiving a doses of 100 Gy, no lesions were observed after 7, 15, 24, 31 , 45 days. However, in all rats sacrified 59, 72 and 90 days after day radiation, a necrotic lesion was always present and confirmed that at each time the lesions were precisely targeted. This apparatus allows precise and reproducible gamma irradiation lesion in rat brain without expensive and time consuming imaging techniques. This device provides a useful system to observe the experimental effects of radiosurgery o n the central nervous system in rats.