Background: Hot cells are used in the production of radiopharmaceuticals to provide radiation workers with a safe environment in which to work. This study was conducted to measure the radiation dose that leaks through the walls of a hot cell.  Materials and Methods: For this study, hot cells of five big hospitals (≥ 1000 beds) in South Korea were selected. To calculate the radiation exposure outside the walls of the hot cell (i.e., the external dose) during fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) synthesis and dispensing activities, exposure rates were measured with a Geiger Muller counter (GM counter) at five locations around the hot cells (10 measurements per each measurement point). Based on the measurements, operating conditions of the hot cells of the five hospitals were conservatively considered to calculate the effective dose. The radiation exposure inside the hot cell (i.e., the internal dose) was estimated considering the operating conditions of the hot cells of five large hospitals as well as international guidelines. Results: The Based on the experimental results, the impact of the internal dose was found to be negligibly low during ¹⁸F-FDG synthesis and dispensing activities (less than 0.21 mSv/y); however, the radiation leakage exhibited levels requiring caution in all directions, with a radiation leakage of up to 19.5 µSv/h measured on the lead glass windows of the hot cells in some hospitals. Conclusion: The conclusion is that radioisotope manufacturers operating radiopharmaceutical synthesis and dispensing hot cells should implement various improvements. Strengthening the shielding of the lead glass windows on the front and sides of cells, implementing real-time dosimetric monitoring, setting dose limits for radiopharmaceutical production processes, and regular worker rotations are needed.