Iodine 131 properties and usages in Brachytherapy - Essay Example

In the testing of the thyroid gland and its functioning, iodine absorption by the cells makes use of iodine 131. Iodine 131 has certain chemical properties. It is a non-metallic, purplish-black crystalline solid. In a process known as sublimation, it can change its state from a solid to a gas directly, without changing into the liquid state. At room temperature it sublimes into a deep violet vapour which irritates the eyes, nose and throat. Iodine 131 dissolves in water or alcohol fairly easily and melts at 236F.

Since it does not remain in its pure state when released, it is generally found as a compound because of its capacity to bind with other elements. In medical treatment, Iodine 131 capsules contain I-131 sodium iodide granules specially produced to be easily swallowed by the patient. The liquid form of Iodine 131 is a clear liquid and is used to diagnose and treat thyroid problems. When a person is exposed externally to large quantities of iodine 131 it can cause burning of the eyes and skin.

Internally, the thyroid gland is affected. This gland utilizes iodine to produce thyroid hormones but is unable to differentiate between radioactive iodine and the more stable iodine. Precautions must be taken when using Iodine 131 as there are harmful effect of gamma radiation, the maximum energy being 0.723 MeV (Bentel p.537). Iodine 131 is administered orally in doses of >100 mCi for thyroid malignancy. Lower doses of 1 to 3 mCi are given for diagnostic reasons. The exposure rate constant for iodine 131 = 2.

2 (R/mCi-hr at 1 cm). Also known as Gamma Factor, exposure rate constant is the exposure rate at a certain distance from a quantity of photon-emitting radionuclide. This constant is commonly used for radiation protection reasons. The following equation calculates the exposure time t at a distance r from the patient. D(t) = (34.6 Q0 Tp (1 - e -0.693t/Tp )) / r2. Here D(t) is the accumulated exposure at time t (in roentgens). 34.6 is the conversion factor of 24hours / day times the total integration of decay (1.44). is the specific gamma ray constant for a point source, R/mCi-hr at 1cm.

Q0 is the initial activity in millicuries of the point source at release time. Tp is the half-life in days. r is the distance from the point source to the subject in centimetres and 't' is the exposure time in days. In the environment, radioactive fallout can cause high concentrations of Iodine 131 which may be absorbed by the body and harm the thyroid gland. To counter the harmful absorption of radioactive iodine, the intake of higher doses of iodine supplements raises the overall quantity of iodine in the body which does not necessitate the absorption and retention in body tissues thereby lessening the assimilation of radioactive iodine.

One historical use of iodine supplements was after the Chernobyl disaster where enormous quantities of radioactive material was released. Iodine supplements protected the population in the vicinity of the disaster from absorbing radioactive iodine. It has been found that with exposure to iodine 131, the risk of thyroid cancer increases but even among those exposed to iodine 131, not many develop thyroid cancer. The highest exposure people received was during the nuclear test explosions in the 1940's.

Although iodine 131 settled on leafy vegetables and fruits, people received