) I-131( T 1/2 = 8.0 days) is used both diagnostically and therapeutically for t
ID: 895840 • Letter: #
Question
) I-131( T 1/2 = 8.0 days) is used both diagnostically and therapeutically for thyroid disorders. Since the radioactivity of an I-131 dose is usually high, it is administered to a patient by fluid (oral or injection). If a patient with a mild thyroid disorder has scheduled an appointment and needs to be administered 200 MBq for the treatment, (a) determine the volume of I-131 (in mL) that the patient must take at 3:00pm. Note that the liquid preparation of I-131 has 100 MBq/mL of activity at 9:00am on the same day. (b) What would be the amount (ng) of I-131 powder you have to dissolve in the solution to give 100 MBq/mL if you were to prepare a 20mLsolution? (c) How long does it take for 80% of the I-131 to decay away after the patient received the injection (in days)?
Please show all work, units and equations!
Explanation / Answer
a) Quantity of dose (in mL) to be dispensed=Activity required / Activity concentration = 200MBq/100MBq/ml=2ml
b) Specific activity (MBq/mg) = 37x3.13x10^9/Axt1/2 = 115.8x10^9 / 131 x24x8 =4.60x10^6 MBq/mg
amount of I-131 powder =20x100 / 4.60x10^6 = 0.4347x10^-6mg=434ng
c)lemda= 0.693/t1/2 = 0.693/8=0.0866
% remaining = 100xe^-lemda t
0.8 = e^-0.0866t
ln0.8 = -0.0866t
-0.223 /0.0866=t =2.576 days
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