Technical note: overprediction of dose with default PRESTA-I boundary crossing in DOSXYZnrc and BEAMnrc.

Use of the PRESTA-I (current default) boundary crossing algorithm for charged particles in DOSXYZnrc and BEAMnrc is shown to result in dose overprediction by up to 2.5% in photon and electron beams (less in high-energy electron beams). The effect is most pronounced when charged particle equilibrium does not exist or when the phantom is not divided into uniform voxels throughout. As a result, the default boundary crossing algorithm in BEAMnrc will be changed to "exact" (single scattering).