Symmetrization of the radiation field inside hohlraum targets for indirectly driven heavy ion beam inertial confinement fusion (ICF) is investigated numerically. The considered targets consist of a casing, enclosing the spherical fuel capsule, and a few cylindrical radiators, schematically representing ion beam irradiated converters. Radiation absorption and remission is dealt with as in the paper by Murakami and Meyer-ter-Vehn, but with the geometry extended to 3-D, and with consideration for the finite size of the radiators. It is found that, for practical casing-to-capsule area ratios (of the order of 10) and converter aspect ratios, two converters cannot provide the uniformity required for ICF. A spherical casing with six converters (placed in couples along the axes of a cartesian coordinate system) could instead illuminate a capsule with non-uniformity well below 2%, which could satisfy the ICF requirements. The effects of changing the area ratio, the size and position of the converters and the geometry of hohlraum are also discussed.