6th International Conference on Computational and Experimental Science and Engineering (ICCESEN) -- OCT 23-27, 2019 -- Antalya, TURKEY GUNAY, Osman/0000-0003-0760-554X WOS:000537521100033 Determination of radiation dose rate is very important for public health and medical workers because the nuclear radiation is hazardous for all. In this study, radiation dose rate was determined after radiopharmaceutical injection for thyroid scintigraphy. Measurements of the dose rate were made at 12 different points: 25, 50, 100, and 200 cm from the patient's head, chest and foot level. Moreover, measurements were made at different times with GM counter to determine the dose rate decay. The amount of radioactivity injected into patients varies between 151 MBq (4.1 Ci) and 192 MBq (5.2 Ci), with average value of 162 MBq (4.4 Ci). The radiation dose rate at 100 cm from the patient's chest level, after 9.16, 28.83 and 49.66 min of injection was calculated as 7.56, 6.35 and 4.73 mu Svh(-1), respectively. After Tc-99m injection, healthcare professionals must be 1 m away from the patient for radiation safety. It was also emphasized that the public should not be in proximity to the patient nearer than 1 m for 3 h after injection.