Are radioactive substances used in medicine always sealed?

Radioactive substances used in medicine are not always sealed. In medical applications, radioactive materials can be found in both sealed and unsealed forms. Sealed sources are typically used in therapies where the radiation is contained, such as in brachytherapy, where radioactive seeds are inserted directly into or near a tumor. However, unsealed radioactive materials can also be used in diagnostics and treatments, particularly in procedures like radioactive iodine therapy for thyroid conditions or in certain types of imaging such as PET scans.

Unsealed sources can pose different safety and handling considerations, as they may be taken up by the patient's body, thereby allowing the radioactive substance to interact with biological systems. This means that while they are utilized in many crucial medical technologies, not all radioactive substances used in medicine are sealed, substantiating the choice that states this fact.