The noble gas used in radiotherapy is xenon. It is used in a type of radiation therapy called brachytherapy, which involves placing radioactive material near the tumor. Xenon is a good choice for brachytherapy because it is a dense gas that can be easily shaped to fit the tumor. It is also a relatively short-lived isotope, which means that it decays quickly and emits less radiation than other isotopes.
Neon, argon, and radon are also noble gases, but they are not used in radiotherapy. Neon is a very light gas that is not dense enough to be used in brachytherapy. Argon is a heavier gas, but it is not as dense as xenon and it is not as short-lived. Radon is a radioactive gas that is found in the environment. It is not used in radiotherapy because it is a long-lived isotope that emits a lot of radiation.
Xenon is a noble gas that is used in a type of radiation therapy called brachytherapy. Brachytherapy involves placing radioactive material near the tumor. Xenon is a good choice for brachytherapy because it is a dense gas that can be easily shaped to fit the tumor. It is also a relatively short-lived isotope, which means that it decays quickly and emits less radiation than other isotopes.