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Radiation Safety Precautions after a Seed Implant

Once the patient's prostate has been implanted, the seeds are left in place permanently, and the patient actually becomes radioactive. Based on the amount of radioactive material implanted, NRC regulations require that patients be given instructions regarding precautions against unnecessary exposure to others. The usual advice: "limit time around children and potentially pregnant women."

The radioactivity from the seeds does not penetrate very far and in fact very little radiation escapes from the surface of the body, so the risk to others is actually quite small. If security becomes more stringent at   airports, the seeds may be picked up (go here.)

A recent study of men after seed implants (Smathers. IJROBP 1999;45:397) measured the dose at the surface of the skin at an average of 5 mrem/hr after I-125 and 1.7 mrem/hr after Pd-103. NRC regulations (go here) set the annual dose limit to the general public at 100 mrem as a safe dose, so a person would have to sit on a man's lap for 20 straight hours after an I-125 implant or 59 hours after Pd-103 to reach this dose. The dose rate at 1 meter from the man is only 0.03 mrem/hr so it would take 1429 hours to reach this dose.

For a pregnant woman, the amount of radiation exposure that is thought to risk harm to the fetus is 5000 mrem. Therefore a pregnant woman would have to sit on a man's lap for days without moving (41 days after I-125 or 122 days after Pd-103) to risk harm to the fetus (staying one meter away it would take 166,666 hours or 6944 days or 19 years to reach this dose (by 19 years hopefully the kid will have moved out of the house.)

In summary, patients should avoid needlessly exposing other people to their radioactivity, but it would take very prolonged exposure at very close distances to expose another person to a significant dose of radioactivity. (for more on radiation safety go here.)