Passage Nuclear Medicine Uses Radiopharmaceuticals for Disease Treatment and as Tracers

Passage
Nuclear medicine uses radiopharmaceuticals for disease treatment and as tracers in medical imaging studies.  Yttrium-90 (⁹⁰Y) is a radiopharmaceutical agent used to treat overgrown joint lining known as pigmented villonodular synovitis, as well as some forms of liver cancer.  It has a half-life of about 64 hours.Although the relatively short half-life of ⁹⁰Y is optimal for use in medical applications, transportation and storage of the radiopharmaceutical are not feasible.  As a result, strontium-90 (⁹⁰Sr) , with a half-life of 28.8 years, is the most common source of ⁹⁰Y.  ⁹⁰Sr is created by a nuclear fission process that begins with uranium-235 (²³⁵U) in a nuclear reactor as shown in Reaction 1.²³⁵U → ⁹⁰Sr + ZReaction 1Fission of ²³⁵U produces ⁹⁰Sr as well as additional fission products (Z) including, but not limited to, technetium-99 (⁹⁹Tc) , iodine-129 (¹²⁹I) , and zirconium-93 (⁹³Zr) .  Figure 1 shows the distribution of fission products.
Figure 1  Distribution of ²³⁵U fission products by atomic weightTo create the final ⁹⁰Y required for nuclear medicine studies, ⁹⁰Sr decay is carried out in a controlled ⁹⁰Y generator.  ⁹⁰Y is then separated from residual ⁹⁰Sr for use in clinical applications.
Adapted from Wheeler CE. Comments on vaccines, August 1987. J Am Acad Dermatol. 1988;18(1 Pt 2) :232-4.
-A patient is injected with 20 ng of ⁹⁰Y.  Assuming yttrium is not excreted, how long will it take for the initial amount of ⁹⁰Y to be reduced to 2.5 ng?

A) 64 hours
B) 128 hours
C) 192 hours
D) 256 hours

Correct Answer:

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