  In this work, we introduce a fast numerical algorithm to solve the
time-dependent radiative transport equation (RTE). Our method uses the integral
formulation of RTE and applies the treecode algorithm to reduce the
computational complexity from O(M^{2+1/d} ) to O(M^{1+1/d} log M ), where M is
the number of points in the physical domain. The error analysis is presented
and numerical experiments are performed to validate our algorithm.
