Accurate estimation of local neuron size of complex 3D neuron structures imaged by microscopy is very important for quantification of neuronal morphology, such as neuron tracing applications. Previously, the Rayburst sampling algorithm was developed to estimate the neuron size in volumetric microscopy images. However, it requires an accurate detection of the neuron centerline, which is not easy and time-consuming. In this paper, we propose to estimate the neuron local radius of any region of interest in a given neuron, by first detecting its corresponding neuron centerline point using Multistencils Fast Marching (MSFM) method and then estimating the local neuron radius by the Rayburst sampling algorithm. The experimental results on different datasets show that the proposed method could obtain very accurate local neuron radius efficiently.