The textbook "Assessment of 99mTc Dose Calibrator Performance in Nuclear Medicine" offers a comprehensive analysis of the performance of dose calibrators used in nuclear medicine. It addresses the precise measurement of radioactivity from gamma and beta radiation, which is essential for the diagnosis and treatment of diseases. The study focuses on applications in nuclear medicine departments in Sudan and includes four quality control tests conducted with the radionuclides 137Cs and 57Co. The results of these tests were compared with international standards to evaluate the accuracy, consistency, linearity, and geometry of the dose calibrators. The findings indicate that all tested calibrators demonstrate good performance and that no correction tables or maintenance measures are necessary.