Spatial distributions of the 3 factors contributing to differences between GBBS and TG-43: source and boundary, applicator, and heterogeneity. The contrast is overridden to muscle, no override, or bone. (a) Top: contribution of source and boundary. Bottom: contribution of applicator. (b) Top row: combination of all three factors. Bottom row: contribution of the heterogeneity. From left to right, the GBBS with solid applicator with contrast overridden to muscle D(Y,N,M,M), contrast not overridden D(Y,N,N,N), or contrast overridden to bone D(Y,N,B,B).