  The quantum version of the Boltzmann transport equation (Wigner-Boltzmann
equation) is a quite useful tool to investigate the effects of energy
dissipation in quantum systems. Numerical approaches uses to be employed in
order to stablish a suitable solution. In this paper, an analytical solution is
shown to exist when the constant relaxation time approximation is considered.
The formalism presented here is capable to avoid some unphysical features early
reported in literature for the conventional boundary condition scheme.
