EGS4 Monte Carlo determination of the beta dose kernel in water

The EGS4 Monte Carlo code has been used to simulate the emission and energy deposition in H 2 O about point sources of monoenergetic electrons and radionuclides of potential use in radioimmunotherapy. The radiations studied were 0.05, 0.1, 0.5, 1.0, 2.0, and 3.0 MeV monoenergetic electrons and 32 P, 67 Cu, 90 Y, 105 Rh, 131 I, 153 Sm, 186 Re, and 188 Re β particles and conversion and Auger electrons. Ten batches of 10 000 electrons (or 10 000 radionuclide decays) each were started isotropically at a point in an infinite homogeneous H 2 O phantom. The parameter–reduced electron–step transport algorithm (PRESTA) version of the EGS4 Monte Carlo code was used to follow these and their progeny, scoring the energy deposited in thin spherical shells. The scaled dose kernels are calculated and compared to kernels available in the literature. These previously published kernels either completely ignore secondary electrons or are based on a Monte Carlo code which improperly sampled the Landau energy straggling distribution.