[en] While conventional Monte Carlo photon transport (MCPT) dose estimation techniques are sufficiently accurate in many cases, they fail when the point of interest is located near media interfaces, since they require the point of interest to be contained by a region of homogeneous medium of several millimetres in diameter. This severely limits the domain of application of MCPT in brachytherapy dosimetry and prevents dose estimation at points such as those immediately behind lead shields contained in gynaecological applicators, or simulation of small intricately structured detector response. The authors successfully adapted to an MCPT code a neutron-flux estimator, the once-more-collided flux estimator (OMCFE), which overcomes this problem. (author)