NEUROPATHOLOGY OF ABLATION OF RAT GLIOSARCOMAS AND CONTIGUOUS BRAIN-TISSUES USING A MICROPLANAR BEAM OF SYNCHROTRON-WIGGLER-GENERATED X-RAYS

Adult-rat-brain tissues display an unusually high resistance to necros is when serially irradiated with parallel, thin slices of a microplana r (i.e., microscopically thin and macroscopically broad) beam of synch rotron-wiggler-generated, approx. 35-120 keV (median approx, 50 keV) G d-filtered X rays at skin-entrance absorbed doses of 312 to 5000 Gy pe r slice. Such microplanar beams were used to irradiate young adult rat s bearing right frontocerebral 9L gliosarcomas (approx. 4 mm diameter) , through a volume of tissue containing the tumor and contiguous brain tissue, either in a single array or in 2 orthogonally crossed arrays of tissue slices. Each array included 101 parallel microplanar slices, 100 mu m center-to-center distance, each slice being approx. 25 mu m wide and 12 mm high, with skin-entrance absorbed doses of 3 12.5 Gy or 625 Gy per slice. Compared with unirradiated controls with a median s urvival time of 20 days after tumor initiation, the median survival ti me was extended in irradiated rats by 139 days (625 Gy, crossed arrays ), 96 days (312.Gy, crossed arrays) or 24 days (625 Gy, single array). The tumors disappeared in 22 of the 36 irradiated rats, 4/11 even alt er unidirectional microbeam irradiation. The extent and severity of ra diation damage to the normal brain in rats with or without tumor was g raded histopathologically. Correlation of those grades with radiation doses shows that loss of tissue structure was confined to beam-crossin g regions and Chat only minor damage was done to zones of the brain ir radiated unidirectionally. (C) 1998 Wiley-Liss, Inc.