Iodine - 131This is a featured page

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Photos: Iodine131-Exposure
How were people exposed to Iodine 131 from Hanford?[15]
Radioactive iodine uptake test is a type of nuclear test performed to evaluate thyroid function. The patient ingests radioactive iodine (I-123 or I-131) capsules or liquid. After a time (usually 6 and 24-hours later), a gamma probe is placed over the thyroid gland to measure the amount of radioactivity in the thyroid gland. The values are then compared.[14]Iodine 131 ingested

 Iodine 131 ablation scan after 24 hours intake of radioactive iodine[16]


Relevant Historical Data: Iodine- 131 is a radioisotope of iodine- an altered form of the element that is chemically the same but is radioactive. I-131 is found as fallout from atmospheric nuclear bomb explosions, along with a variety of other radioactive substances such as strontium-90. People were exposed by drinking contaminated milk, where is was absorbed by the cows in the pastures. Also contaminated were eggs and leafy vegetables. I-131 has been of the greatest concern because it concentrates in the thyroid, particularly in children, and may increase the risk for thyroid cancer. There appears to be little risk for people exposed as adults. Because iodine concentrates in the thyroid, high doses of I-131 are used to treat some types of benign thyroid diseases as well as thyroid cancer.[1]

In 1811, Bernard Courtois discovered natural iodine in water that was used to dissolve certain parts of seaweed ash for use. Radioactive iodine-131 was discovered by Glenn T. Seaborg and John Livingood at the University of California - Berkeley in the late 1930's.[8]
Chemical/Radioactive Composition: Stable iodine (iodine-127) is naturally present in seaweeds, sponges, other materials, and also found in Chilean saltpeter, caliche, and brine associated with salt deposits. It is present in nature in various materials, with soil, rock, and all living organisms containing low concentrations. Radioactive isotopes of iodine are produced by nuclear fission. When an atom of uranium-235 (or other fissile nuclide) fissions, it generally splits asymmetrically into two large fragments – fission products with mass numbers in the range of about 90 and 140 – and two or three neutrons. (The mass number is the sum of the number of protons and neutrons in the nucleus of the atom.) Iodine-129 and iodine-131 are two such products. The fission yield of iodine-129 is about 1% and the yield of iodine-131 is close to 3%. That is, about one atom of iodine-129 and three atoms of iodine 131 are produced per 100 fissions. [5]

Pure I-131 is a non-metallic, purplish-black crystalline solid. However, because it readily binds with other elements, I-131 usually is found as a compound rather than in its pure form.9]
Energy Characteristics: I-131 decays with a half-life of 8.02 days with beta and gamma emissions. This nuclide of iodine atom has 78 neutrons in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I transforms into 131Xe:The primary emissions of I-131 decay are 364 keV gamma rays (81% abundance) and 606 keV beta particles (89% abundance).[3] Mean beta energy is 192 keV.[10]
Exposure Rate Constant: 2.3 R/Hr at 1cm per mCi [4]
Half-life Properties: 8 Days [4] Biological Half-Life: 138 days* Effective Half-Life: 7.6 days* * These are “generic” biological and effective half-lives; the specific labeled compound may alter.[11]
Forms available for use: Derived from Iodine into a liquid form which is swallowed.[2]
I-131 is also available in capsule form.[10]
HVL in lead: .31 cm [4] HVL of 6.3 cm in water.[10]
Measurement/Calibrations/QA: Survey Instrumentation [11]
  • Survey meter equipped with a G-M pancake or thin-window probe is efficient for detecting the betas from I-131.
  • Survey meters equipped with a NaI scintillation probe is suitable for detection of the I-131 gamma.
  • Either a gamma counter or a liquid scintillation counter can be used to detect removable I-131 contamination on wipe tests smears.
Calibration [12]
  • Begins with a radioactive preparation- commonly in solution- of the radionuclides in a stable chemical form.
  • Specific activity of the solution must not be modified by any change other than the normal radioactive decay of the nuclide. Then the specific activity of the solution is determined (number of disintegrations per second which take place in the solution per unit of mass).
  • The preparation is then enclosed in a sealed ampoule and dispatched to the requesting lab.
  • The distributor gives a certificate of the specific activity of the sample at a date (reference date) some days after the sample is due to reach the client- usually about a week later. This ensures that the receiving lab will be able to do its work with the sample on that date.
QA [13]
  • At the designated time, the dose to be administered is brought on a cart to the patient's room in its shielded shipping container. All contamination precautions must be observed,
  • If liquid I-131 is used for therapy, appropriate use of a closed-circuit liquid delivery system may limit or eliminate contamination of the ambient air and skin and the possibility of any accidental spillage.
Used in formula/calculation: Typical dosage for hyperthyroidism is 5-10 mCi of I-131 sodium iodide.
Typical dosage for thyroid cancer is 100 -200 mCi of I-131 sodium iodide.[10]
Uses in Radiation Oncology: Mostly used for the treatment of hyperthyroidism, which can be caused by Graves disease. This is an overactive thyroid problem or caused by nodules within the gland producing too much thyroid hormone. This is usually treated by a nuclear medicine department.
Iodine-131 is also used to treat thyroid cancer.[2]
Treatment Planning: This procedure is primarily done in nuclear medicine departments. Treatment planning information could not be obtained.

Most nuclear physicians prefer fixed dose I-131 therapy without actually calculating the dosimetry for ablation. The treatment dose variances among different centers are wides with a range of 25-200 mCi, depending on whether it is given for residual functioning thyroid tissue in the the neck or for metastases detected locally in the neck or in various organs as well as the age and gender of the patient. First doses as high as 300mCi have been given in some centers on the basis of assumption that metastases may lose their ability to concentrate iodine. With high-dose therapy, the dose to the blood should be less than 200 rad to reduce bone marrow toxicity. The total whole body retained dose at 48 hours should be less than 120 mCi in widespread metastatic thyroid carcinoma and 80 mCi in the presence of lung metastases. The latter is a precaution to avoid inducing pulmonary fibrosis. [13]
One other interesting fact: Iodine- 131 is a decay product of Te-131 (beta-) and decays down to
Xe-131 (beta-).[6] Half Value Thickness in water is 6.3 cm.

Iodine is a nonmetallic, purplish-black crystalline solid. It has the unusual property of ‘sublimation,' which means that it can go directly from a solid to a gas, without first becoming liquid. It sublimes to a deep violet vapor at room temperature. This vapor is irritating to the eyes, nose and throat. Iodine dissolves in alcohol and in water. It melts at 236 °F.[8] I-131 dissolves easily in water or alcohol. I-131 readily combines with other elements and does not stay in its pure form once released into the environment.[9]


Links:
http://www.bt.cdc.gov/radiation/isotopes/iodine.asp
http://www.epa.gov/rpdweb00/radionuclides/iodine.html
http://www.ead.anl.gov/pub/doc/Iodine.pdf
http://www.iodine131.org
http://en.wikipedia.org/wiki/Iodine-131
References:
1. National cancer institute. Available at: http://www.cancer.gov/cancertopics/factsheet/I131qa. Accessed March 16, 2009.
2. Radiology Info. Available at: http://www.radiologyinfo.org/en/info.cfm. Accessed March 16, 2009.
3. Iodine 131. Radioactive Isotopes. Availabe at http://ie.lbl.gov/decay.html. Accessed March 15, 2009.
4. Bentel, G. Radiation Therapy Planning. 2nd Ed.NewYork:Macgraw-Hill:1992. pp.534-535.
5. Argonne National Laboratory, EVS. Iodine. Human Health Fact Sheet. August 2005. Available at: http://www.ead.anl.gov/pub/doc/Iodine.pdf. Accessed March 17, 2009.
6. Wiipedia. Available at: http://en.wikipedia.org/wiki/Iodine-131. Accessed March 17, 2009.
7. Argonne National Laboratory. Available at: http://www.ead.anl.gov/pub/doc/tbl2-rad-prop.pdf. Accessed March 17, 2009.
8. U.S. Environmental Protection Agency. Radiaton Protection. Iodine. Available at: http://www.epa.gov/rpdweb00/radionuclides/iodine.html. Accessed on March 19, 2009.
9. Centers for Disease Control and Prevention. Iodine 131. Available at: http://www.bt.cdc.gov/radiation/isotopes/iodine.asp. Accessed on March 19, 2009.
10. Jani, Shirish K. Handbook of Dosimetry Data for Radiotherapy. CRC Press, Inc., 1993, p. 149.
11. University of Cincinatti. Radiation Safety:I-131. Available at: http://researchcompliance.uc.edu/radsafety/isotope/isds-I131.html. Accessed on March 19, 2009.
12. International Atomic Energy Agency. Calibrated Nuclides-An IAEA Service. Available at: www.iaea.org/Publications/Magazines/Bulletin/Bull062/06206802325.pdf. Accessed on March 19, 2009.
13. Al-Shakhrah, IA. Radioprotection using Iodine-131 for Thyroid Cancer and Hyperthyroidism: A review. Clinical Journal of Oncology nursing. 2008; 12: 905-912.
14. New York Times. Radioactivity Test. Available at: http://www.cdc.gov/.../htdsweb/Iodine131_Exposure.htm. Accessed on March 23, 2009.
15. Then Handford Tyroid Disease Study. Iodine 131 Exposure. Available at: www.cdc.gov/.../htdsweb/Iodine131_Exposure.htm. Accessed on March 23, 2009.
16. Chemical Forums: A Socratic Model of Chemical EducationAvailable at: www.chemicalforums.com/index.php?topic=15248.0. Accessed on March 23, 2009.

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