Ionizing radiation is used in radiotherapy to treat cancer and to sterilise medical equipment because it destroys cells. Basic objective of this lecture is to present on Using Ionizing Radiation in Medicine. There are 3 main uses of ionizing radiation in medicine: Treatment, Diagnosis and Sterilisation. This lecture briefly describe one medical use of radiation based on the fact that that it can destroy cells (instrument sterilisation, treatment of cancer). Here also describe one medical use of radiation based on the fact that radiation is easy to detect.