  Thermal dust emission carries information on physical conditions and dust
properties in many astronomical sources. Because observations represent a sum
of emission along the line of sight, their interpretation often requires
radiative transfer modelling.
  We describe a new radiative transfer program SOC for computations of dust
emission and examine its performance in simulations of interstellar clouds with
external and internal heating.
  SOC implements the Monte Carlo radiative transfer method as a parallel
program for shared memory computers. It can be used to study dust extinction,
scattering, and emission. We tested SOC with realistic cloud models and
examined the convergence and noise of the dust temperature estimates and of the
resulting surface brightness maps.
  SOC has been demonstrated to produces accurate estimates for dust scattering
and for thermal dust emission. It performs well with both with CPUs and with
GPUs, the latter providing up to an order of magnitude speed-up. In the test
cases, ALI improved the convergence rates but also was sensitive to Monte Carlo
noise. Run-time refinement of the hierarchical-grid models did not help in
reducing the run times required for a given accuracy of solution. The use of a
reference field, without ALI, works more robustly. It also allows the run time
to be optimised if the number of photon packages is increased only as the
iterations progress.
  The use of GPUs in radiative transfer computations should be investigated
further.
