  Context. Time-dependent, 3D radiation transfer calculations are important for
the modeling of a variety of objects, from supernovae and novae to simulations
of stellar variability and activity. Furthermore, time-dependent calculations
can be used to obtain a 3D radiative equilibrium model structure via relaxation
in time. Aims. We extend our 3D radiative transfer framework to include direct
time dependence of the radiation field; i.e., the $\partial I/ \partial t$
terms are fully considered in the solution of radiative transfer problems.
Methods. We build on the framework that we have described in previous papers in
this series and develop a subvoxel method for the $\partial I/\partial t$
terms. Results. We test the implementation by comparing the 3D results to our
well tested 1D time dependent radiative transfer code in spherical symmetry. A
simple 3D test model is also presented. Conclusions. The 3D time dependent
radiative transfer method is now included in our 3D RT framework and in
PHOENIX/3D.
