Magnetic resonance diffusion tensor imaging study of rhesus optic nerve radiation injury caused by a single dose/fractionation scheme stereotactic radiosurgery at an early stage

Summary Background and purpose Radiation-induced optic neuropathy (RION) is a devastating late complication of radiotherapy. However, research on the imaging performance of RION is not sufficient. The aim of this study was to investigate the performance of magnetic resonance diffusion tensor imaging (DTI) early after injury of the optic nerve of rhesus monkeys by a single-dose/fractionation-scheme of stereotactic radiosurgery (SRS). Materials and Methods The intraorbital optic nerve contour of 5 rhesus monkeys was acquired by magnetic resonance imaging (MRI). Then, the unilateral intraorbital optic nerves of 5 rhesus monkeys were injured by gamma knife surgery (GKS) with a single-dose/fractionation scheme (marginal dose of 15 Gy, 50% isodose curve). DTI was performed before the irradiation and 1 week, 2 weeks, 4 weeks, and 24 weeks after injury to obtain the cross-sectional area, and the fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD) and radial diffusivity (RD) values. Results The cross-sectional area of the injured optic nerve exhibited significant atrophy 24 weeks after SRS. FA declined 1 week after injury; this value then increased slightly but remained lower than before injury ( P < 0.05). AD began to decline in the 2 weeks after injury and gradually disappeared ( P < 0.05). Conclusion SRS with a single-dose/fractionation scheme (marginal dose of 15 Gy, 50% isodose curve) on the unilateral intraorbital optic nerve can induce RION. DTI can detect RION at an early stage. FA and AD are useful indicators for RION diagnosis. In the early stage, the primary site of RION may be the vascular endothelium.