The Uses of Iridium 192 in Brachytherapy

Radioactive Isotope Report

Iridium-192 (19277Ir) is a radioactive isotope that is created synthetically.

An iridium-192 atom contains 77 protons, 115 neutrons and 77 electrons.

It is formed via neutron activation, usually in nuclear reactors.

Iridium is a member of the platinum family and is often found in large platinum reserves. Iridium is the most corrosion-resistant metal,

at temperatures up to 2000oC. . Iridium has two main naturally occurring

isotopes. These are Iridium-191 and Iridium-193, with Iridium-193 being

the more abundant. Smithson Tennant discovered Iridium in residue left

over in a platinum solution after it had been dissolved in aqua regia. In

this residue he also discovered osmium.

Iridium-192 has a half-life of 73.83 days and decays to either Platinum-192 (96%) or Osmium-192 (4%). The reason it decays into two products is it normally decays through beta and gamma radiation emission, becoming Platinum-192. However sometimes the beta particles are absorbed by other iridium atoms, causing them to become Osmium-192.

Iridium-192 is used in the treatment of cancer in a branch of radiation therapy called HDR (high dose rate) brachytherapy. Pierre Curie first suggested the use of radiation in this way in 1901 and Alexander Graham Bell also suggested this independently. Iridium-192 is used in HDR brachytherapy because it has a high specific activity per unit mass. In this form of cancer treatment a small amount of iridium-192 is placed inside a capsule which is in turn placed in or near the tumor using needles or catheters. It then continues to emit radiation into the tumor causing it to die. Careers that use Iridium include radiation therapists, medical physicists and radiation oncologists. Radiation oncologists are doctors who prescribe the use of the radioisotope to treat cancer. Radiation therapists are the people who plan how to deliver the iridium into the body and deliver the radiation. Finally the medical physicists are the professionals in charge of ensuring that the radioisotopes are at an acceptable activity level.

The use of Iridium in the field of HDR brachytherapy has a number of positives that I believe outweigh the negatives. Some of these positives include its high specific activity, which means that a small amount can produce a lot of radiation. This makes it ideal for HDR treatment as you only need a small amount to produce a significant amount of radiation. One downside to Iridium is its relatively short half-life. A short half-life means that it has to be replaced sooner than an isotope with a long half-life; however, in High Dose Rate treatment this negative is far outweighed by the positive of Iridium-192's high specific activity. This allows a short treatment time so many patients can be treated per day. As for the safety of iridium-192 it has been tested and the amount of unwanted radiation exposure was negligible. This shows that iridium-192