Hyperthyroidism is caused by growth of tumor-like cells that secrete thyroid hor
ID: 169198 • Letter: H
Question
Hyperthyroidism is caused by growth of tumor-like cells that secrete thyroid hormones in excess of normal amounts. If untreated, an individual with hyperthyroidism may experience extreme weight loss, anorexia, muscle weakness, heart disease, and intolerance to stress and eventually may die. The most successful and least invasive treatment option is generally considered to be radioactive iodine-131 therapy. This involves the injection of a small amount of radioactive iodine into the body. For the type of hyperthyroidism called Graves' disease, it is usual for about 40% to 80% of the administered radioactive iodine to concentrate in the thyroid gland. For functioning adenomas ("hot nodules"), the uptake is closer to 20% to 30%. Excess iodine-131 is excreted rapidly by the kidneys. The quantity of radioiodine used to treat hyperthyroidism is not enough to injure any tissue except the thyroid, which slowly shrinks over a matter of weeks to months. Radioactive iodine is either swallowed in a capsule or sipped in solution through muscle a straw. A typical dose is 5 to 15 millicuries. The half- life of iodine-131 is eight days. a. Suppose that it takes forty-eight hours for a shipment of iodine-131 to reach a hospital. How much of the initial amount shipped is left once it arrives at the hospital? b. Suppose a patient is given a dose of 10millicuries, of which 30% concentrates in the thyroid gland How much is left one week later? c. Suppose a patient is given a dose of 10 millicuries of which 30% concentrates in the thyroid gland. How much is left thirty days later?Explanation / Answer
Half life is the term used to define time taken by a substance to get reduced to half of its initial quantity.
Given half life of radioactive idoine 131 is 8 days.
a. Time taken by the shipment to reach the hospital is 48 hours i.e. 2 days.
It takes 8 days for Iodine-131 to get reduced to half,
in 4 days it will be reduced to 1/4th and
in 2 days 1/8th of the initial shipment will be lost i.e. . 2.5%.
100-12.5 = 87.5
So 87.5% of the initial amount of Iodine-131 will be left by the time the shipment reaches the hospital.
b. A patient was given 10 millicuries.
30% of its is absorbed by thyroid gland which equals to 3 millicuries.
70% i.e 7 millicuries(mc) is remaining in blood.
As given half life is 8 days, 7mc will be reduced to 3.5mc after 8 days.
Per day 0.4375mc will be lost.
So in 7 days,
7*04375= 3.06 mc will be lost.
Remaining substance in blood is,
7.5 - 3.06 = 3.94 millicuries
After one week, 3.94 millicuries is left in the blood after a week
c. After 30 days the remaining substance in the blood will be _________. ( Initially 7 millicuries is left in blood)
In 30 days there will be 3 half life reductions.
In the first week 7 mc will be reduced to 3.5 mc
In the second week 3.5mc will be reduced to 1.75mc
In the third week 1.75mc will be reduced to 0.875mc
Now if we consider the remaining 0.875mc as initial amount it gets reduced to 0.4375 in the next 8 days at 0.054mc/day.
So in 6 days ( 30 days = 3 weeks + 6days)
6 * 0.054 = 0.324mc will be reduced.
Remaining is
0.875 -0.324 = 0.551 millicuries
So 0.551 mill curies of Iodine-131 will be remained in the patient's body after 30 days.
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