Question

given a radiotracer Technetium-99m with a half-life of 6 hours and a photon energy of 140 keV or an Iodine-131 with a half-life of 8.04 days and a photon energy of 364 keV, which one would be better to use on a patient if you wanted to take one 30-minute image a day to track a new cancer therapy over 6 days? Explain your answer.

Answer 1

Even though, Tc -99 emits lower energy radiation it is not suitable for a study of 6 days. Since the lifetime of Tc-99 is 6 hours. The processes taking place in relatively fast processes we can use this isotope. The biological half-life of Tc-99 is 1 day.

For studying a cancer therapy for 6 days, it is better to use I-131. Even after 6 days, considerable count of radiation we can detect from this isotope since its half-life is 8 days. Whereas in the case, it is very difficult to get a considerable signal intensity after 2 days. Thus I-131 isotope is better for this purpose.