A new method has been proposed for calculating the dose rate around a radioisotope reservoir tank using EGS4(Electron Gamma Shower Version4).Several improvements,such as uniform distribution of the radioactive substances in the reservoir tank and shielding effect by the tank wall,were made for more accurate determination of the activity-todose rate conversion coefficients.The Monte Carlo code EGS4 was employed in this report,and the cumulative dose around the reservoir tank was calculated.The results of calculations are useful for a design for radiation safety management in PET(positron emission tomography)facilities.