MadSci Network: Medicine

Re: seed radiation - why do you have to be away from small children?

Date: Tue Mar 30 14:40:56 2004
Posted By: John Moulder, Professor of Radiation Biology
Area of science: Medicine
ID: 1080591203.Me

prostate implant radiation safety

Lisa, you ask:

"My father in law recently had seed radiation for prostate cancer and his doctor advised him to avoid close contact with young children or pregnant women for several weeks. Why? What will happen to the young child or women? He takes care of my 15 month old from 8am to 5pm Monday thru Friday, should I be worry?"

There are basically three kinds of radiation treatment for cancer:

  1. "External beam" radiation therapy where patients are treated with beams of radiation coming from x-rays machines, linear accelerators or very large radioisotope sources.
  2. Removable "implants" where small radioactive sources are placed in or around the tumor for minutes or days and are then removed. Patients generally (always?) remain in the hospital while the radioactive sources are in their bodies.
  3. Permanent "implants" where radioactive material is placed in or around the tumor and left there permanently. Most of the radiation produced by these permanent implants does not get out of the body and even the small amount that get out decreases over the weeks after the seeds are put in.

For the first two types of radiation treatment, the patient is not radioactive after the procedure is done. But for the third type, the permanent implants, the patients are still radioactive when they are sent home. The "seed radiation" done for prostate cancer is this type of radiation treatment.

Most jurisdictions, including the US, have strict regulations concerning how much radiation can be safely received by other people who might be near the radioactive patient. In particular they regulate how much radiation would be received by the most radiation-sensitive individuals in the population (namely fetuses and children).

To estimate when the radiation level in a patient is "low enough" radiation physicists need to make some assumptions about how much time the patient will be close to children and pregnant women. Generally they assume that the patient will keep their distance, and instruct them to do this.

Here are some typical instructions to patients who have received prostate seed implants.

From the Canadian Association of Radiation Oncologists:

"Iodine 125 emits very low-energy radiation which does not travel far; in fact, the vast majority of the radiation is stopped inside the prostate itself and only a tiny fraction escapes beyond the body. However, very small amounts of radiation can reach other people from either a seed being passed in the urine or by a tiny amount of radiation that escapes from the prostate and travels through the air. The amount that escapes is so small that it is not considered a risk for most people, however small children and pregnant women may be more sensitive to the effects of radiation, and therefore, we recommend some additional precautions for these people when around the patient during the first two months following an the implant. You should avoid prolonged close contact with young children during this time eg. child sleeping on your lap. You should avoid sleeping with a woman who is pregnant."

From the Mayo Clinic in the US:

"The radiation sources used to treat prostate cancer (Iodine-125 and Palladium-103) are low-energy radioactive sources. This means that the majority of radiation that they give off is delivered only over a short distance (less than an inch from each seed). Once the radiation seeds are in place, the radiation emitted to tissues surrounding the prostate and to other people is minimal. However, because the radiation used to treat prostate cancer and all other cancers has the potential for damaging healthy cells (as well as the cancer cells), it is advisable to limit radiation exposure to healthy individuals (especially children and the unborn).
"The Nuclear Regulatory Commission requires no special precautions for patients receiving radiation seed implants after they leave the hospital. However, the following precautions are advised for the first two months after the implant procedure:
1. Limit close contact (less than six feet) with children and pregnant (or possibly pregnant) women. Children should not sit on a subject's lap for extended periods of time..."

If anyone is really curious, the precise regulations for this issue in the US can be found on the Nuclear Regulatory Commission website.

John Moulder
Radiation Biologist
Medical College of Wisconsin

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