You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which one of the following radioisotope is not used as permanent implant in brachytherapy? and explain in detail?
Cesium 137 is used as a temporary implant and not a permanent implant. It is used almost exclusively for low dose rate brachytherapy. In low dose rate brachytherapy, temporary implant which is the source of low energy radiation is kept adjacent to the tumor. Temporary implants are commonly used in head and neck cancer. It is used as an interstitial implant in which sources are loaded through catheters implanted into the tumor volume. Most commonly used temporary radioisotope is Ir 192. Ref: Brachytherapy: Applications and Techniques By Phillip M. Devlin, Page 52; Radiation in Medicine: A Need for Regulatory Reform By U.S. Nuclear Regulatory Commission, Page 71