Dose distribution in water for monoenergetic photon point sources in the   energy range of interest in brachytherapy: Monte Carlo simulations with   PENELOPE and GEANT4
  Monte Carlo calculations using the codes PENELOPE and GEANT4 have been performed to characterize the dosimetric properties of monoenergetic photon point sources in water. The dose rate in water has been calculated for energies of interest in brachytherapy, ranging between 10 keV and 2 MeV. A comparison of the results obtained using the two codes with the available data calculated with other Monte Carlo codes is carried out. A chi2-like statistical test is proposed for these comparisons. PENELOPE and GEANT4 show a reasonable agreement for all energies analyzed and distances to the source larger than 1 cm. Significant differences are found at distances from the source up to 1 cm. A similar situation occurs between PENELOPE and EGS4. 
Julio F. Almansa, Rafael Guerrero, Feras M.O. Al-Dweri, M. Anguiano   and A.M. Lallena