OBJECTIVES: To describe the chronic ocular lesions associated with microbeam radiation therapy (MRT) in an experimental rat study. PROCEDURES: MRT was administered bi-directionally with a skin entry dose of 350 Gy. During laterally directed irradiation, the beam entered the head on the right with the center of the beam array 3 mm posterior to the center of the right eye. During irradiation in anterior-posterior direction, the right eye was almost completely in the path of the beam array. Twelve months after MRT ophthalmic examinations were completed on 37 treated (MRT+) and 16 control (MRT-) rats. Electroretinography (ERG) was completed in two MRT+ and one MRT- rat. Histopathology was performed on eyes of 16 MRT+ and 9 MRT- rats, and retinal and choroidal thicknesses were measured. RESULTS: Biomicroscopic and indirect ophthalmoscopic examinations revealed fundus pallor and retinal vascular attenuation in 33 of 37 right and 2 of 37 left eyes of MRT+ rats. Cataracts were present in the right eyes of 12 of 37 MRT+ rats. ERG amplitudes were reduced in the eyes of MRT+ rats. Light microscopy revealed retinal lesions ranging in severity with loss of outer to inner retinal cell layers, in 16 of 16 right and of 8 of 16 left eyes MRT+ rats. The mean right retinal thickness of MRT+ rats was reduced. CONCLUSIONS: Eyes within the field treated with MRT at a dose of 350 Gy develop retinal degeneration and occasionally, cataract.
OBJECTIVES: To describe the chronic ocular lesions associated with microbeam radiation therapy (MRT) in an experimental rat study. PROCEDURES: MRT was administered bi-directionally with a skin entry dose of 350 Gy. During laterally directed irradiation, the beam entered the head on the right with the center of the beam array 3 mm posterior to the center of the right eye. During irradiation in anterior-posterior direction, the right eye was almost completely in the path of the beam array. Twelve months after MRT ophthalmic examinations were completed on 37 treated (MRT+) and 16 control (MRT-) rats. Electroretinography (ERG) was completed in two MRT+ and one MRT- rat. Histopathology was performed on eyes of 16 MRT+ and 9 MRT- rats, and retinal and choroidal thicknesses were measured. RESULTS: Biomicroscopic and indirect ophthalmoscopic examinations revealed fundus pallor and retinal vascular attenuation in 33 of 37 right and 2 of 37 left eyes of MRT+ rats. Cataracts were present in the right eyes of 12 of 37 MRT+ rats. ERG amplitudes were reduced in the eyes of MRT+ rats. Light microscopy revealed retinal lesions ranging in severity with loss of outer to inner retinal cell layers, in 16 of 16 right and of 8 of 16 left eyes MRT+ rats. The mean right retinal thickness of MRT+ rats was reduced. CONCLUSIONS: Eyes within the field treated with MRT at a dose of 350 Gy develop retinal degeneration and occasionally, cataract.