Monte Carlo Algorithms are slowly establishing themselves in Treatment Planning. They are now mature enough (and PCs are fast enough) for routine clinical use. The Electron MonteCarlo (eMC) algorithm is Varian's implementation for Electron dose calculation in the Eclipse Treatment Planning System. We implemented the eMC in 2006. 

A 20MeV electron beam modeled finer and finer by increasing the number of histories. The beam passes through a 1x1cm hole in a 1.5cm thick cerrobend applicator insert. As the number of particle histories is increasing, the 1x1cm "pencil beam" gets modeled better and better by the algorithm. The loop has images with 10k, 20k, 50k, 100k, 500k, 1M, 5M, and 10M particles. 1% relative uncertainty of the mean dose will be reached after 47480000 particles and a calculation time of 1171 seconds on average PC hardware. The 10% isodose surface is drawn in white. Click to enlarge. The corresponding transversal plane can be seen here. 