Interaction of ionizing radiation causes ionization and excitation in atoms and molecules at biological system and production a number of deleterious and abnormal productions in a living system. Having advers effects of ionizing radiations necessitate exact determination of administrative amounts and patient doses, in order to prevent impermissible exposures of patients and theirs surroundings. Accurate calculation of radiation dose requires accurate data about the physical deacay characteristics of the radionuclide and its distribution in the body. On the other hand, the biologic function of different tissues of human body is different among persons. Therefore, there is the variability of the biological response of different individuals to the same radiation dose. How does on compute the total dose the patient form the time of administration (t=0) to the time when the dose rate has finally been reduced to zero In this article, our goal is the calculation and determination of dose in patients and providing the protectoral survey. In nuclear med clear procedures it is almost impossible to measure the radiation dose directly using any kind of radiation detection. Instead, this has to be calculated by using a variety of physical and biological data and special mathematical equations. An approach to determined radiation doses is the absorbed fraction method. This is the proceeded in four steps: calculation of the rate of energy emission by radionuclide in the source volume (s), calculation of the energy absorption by the target volume (T), calculation of the average dose rate (dD/dt), and calculation of the average dose D. That finally results dose. The overall expression may be used. D(T¬S)=(1.44).F.A0.T1/2(eff) .s(T¬S) radWhere S factors is the dose rate form I mCi activity. It depends only on the phisical data that biokinetics of the radionuclidic distribution is more complex, and the uptake in the oragan is instantaneous, on the other hand, the disapperance of the radioactivity from the source doesn't have a single exponential term. In the case of a radiopharmaceutical with complex biokinetics, for radiation dose valculations, cumulated activity A needed for radiation dose calculations is determined by either graphic methods or multiexpontial curve-fitting methods. Then, Cumulated activity A in each organ may be calculated from the actual biokinetic data:The physical data such as radiations emitted by a radionuclide and the absorbed fractions for various source and target combinations of a standard main into on single term, 'S" factor, for radionuclide’s used in nuclear medicine, dose rate is nearly equivalent to the absorbed dose and can uses the principle of reducing exposure to the body, that is distance, time, and adequate shielding, to provide the ALARA.E(R) = (N.GAMMA/d2). em(linear)++x.tTherefore, it may provide necessarily safety in nuclear medicine by observing of protection principles and by mindfully application of radioisotopes and this increase the advantage of using ionizing radiation against on deleterious effects.