20 milicuries of iodine 131 in sieverts?

[microcurie]

HI there I was searching on how to convert mci to sv and the only search result is from this foruns

A family member took iodine 131 for graves desease, and I was wondering how much radiation she took.

She took a 20 milicuries capsule and was told to not come in close proximity with other people for more than 2 hours, among other requirements.

Now I was wondering: what is the total amount of SV she got? What is the amount of SV someone else would get for each hour spent around her?

I've found this:

The radiation received by the thyroid and gonads during 131I therapy of thyrotoxicosis can be estimated from the following formula:

Total beta radiation dose = 73.8 x concentration of 131I in the tissue ('Ci/g) x average beta ray energy (0.19 meV) x effective isotope half-life

For illustration, we can assume a gland weight of 50 g, an uptake of 50% at 24 hours, a peak level of circulating protein-bound iodide (PB 131I) of 1% dose/liter, an administered dose of 5 mCi, a thyroidal iodide biologic half-life of 6 days, and a gamma dose of about 10% of that from beta rays. On this basis, the thyroid receives almost 4,100 rads, or roughly 1,600 rads/mCi retained. The gonadal dose, being about one-half the body dose, would approximate 2 rads, or roughly 0.4 rads/mCi administered.

here: http://www.thyroidmanager.org/Chapter11/chapter11.htm

They were speaking about mice in the previous paragraphs, and it says "50g" for thyroid weight so maybe this doesn't work for humans, either way I don't know how to use the formula

 

[Reno Deano]

There is no direct conversion except by internal dose calculations. mCi is material and SV is dose. Many forums on medical dosimetry probably have rules of thumb for mCi taken in on therapy or diagnostic uptakes.

Here is a link: (Must convert MBq to microCi and it only gives Thyroid absorbed dose (grays))

http://www.jsnm.org/files/paper/anm/ams182/ANM18-2-09.pdf"

 

[minerva]

Calculating that person's internal doses is a little bit tricky, but what about the external gamma dose received by another person standing near the patient who took the ¹³¹I?

Let's just ignore the distribution of the ¹³¹I in the person's body, and assume that it stays as a point source.

http://www.radprocalculator.com/Gamma.aspx

You should get 36 uSv/h at a distance of 1 m.

 

[microcurie]

Thanks for the reply!

IfI understand correctly that is only right after she ingested the pill, right? Aftards it would be lower, correct?

 

[Reno Deano]

Iodine 131 has a short half-life (8 days) an is quickly secreted from the body, except that taken up by the thyroid. Regulations require the patient and family to follow safety rules for using bathrooms, mingling, and habitation. The dose received from people near by is inconsequential. It really gets complicated if the it is a women and she is pregrent or nursing a baby, in-which the procedure should not be done.

 

[minerva]

When a patient takes a radiopharmaceutical, the rate of elimination of the radioactivity from the person's body is actually dependent on two factors - the radionuclide's physical half-life, and the biological half-life of the radiopharmaceutical. It's really just a matter of multiplying together both exponential decay terms (or adding together the two decay constants.)

Some of the radionuclide will decay while it's still inside the patient's body, and some of the radiopharmaceutical will be eliminated biologically before it has decayed.

Different radiopharmaceutical compounds that contain the same actual radionuclide (for example Tc-99m, which has lots of different uses involving different kinds of compounds) will have different rates of elimination of the radioactivity from the patient, even though the physical half-life is of course the same, because the rate of biological metabolism and elimination of the compound will be different.

what is the total amount of SV she got? What is the amount of SV someone else would get for each hour spent around her?

To be honest, whenever you have a nuclear medicine procedure, if you want to ask the nuclear medicine technologist or radiopharmacist or whoever is administering the stuff "What radiological dose will this give me?" I expect that you should be able to get a no-nonsense answer. They should have a fairly good idea, and if they don't, I would hardly trust them to prepare and administer a radiophamaceutical.

 

[daveb]

To be honest, whenever you have a nuclear medicine procedure, if you want to ask the nuclear medicine technologist or radiopharmacist or whoever is administering the stuff "What radiological dose will this give me?" I expect that you should be able to get a no-nonsense answer. They should have a fairly good idea, and if they don't, I would hardly trust them to prepare and administer a radiophamaceutical.

In addition, for actual drugs such as sestamibi or the like, the package insert from the manufacturer should have the expected dose per unit activity listed for both whole body as well as target organs. You can also find information here. http://www.radiochemistry.org/nuclearmedicine/frames/radiopharm_dosimetry/adult_dose.html"