Consideration for a revised Gaussian-pencil-beam-model reported for calculation of the in-water dose caused by clinical electron-beam irradiation

Purposes: We perform further development for our previous Gaussian-pencil-beam-model used for calculating the electron dose in water under clinical electron-beam irradiation. The main purpose is to evaluate accurately the parallel beam depth-doses at deep depths beyond about the extrapolated range (Rp) under an infinite field. Methods: Sets of parallel beam depth-doses under an infinite field were reconstructed for the same beams of E=6, 12, and 18 MeV in light of the electron Monte Carlo (eMC) datasets as reported by Wieslander and Knöös (2006), separating the datasets into the direct electron beam and direct-plus-indirect electron beam groups. Particularly, for each electron beam, we took serious views of the depth-dose (DD) curves near the beam entrance surface and of the OAD (off-axis dose) curves at deep depths beyond about the extrapolated range (Rp) under an infinite field. Results and conclusions: The following results were obtained by comparing the calculated DD and OAD datasets with the eMC datasets: (i) The revised Gaussian pencil beam model is of practical use without using complicated correction factors; and (ii) The DD and OAD datasets are yielded effectively over wide ranges of depths and off-axis distances, respectively.