Workers in nuclear medicine may be exposed to radiation from unsealed sources either through external irradiation or through radioactive substances entering the body. The primary precautions for external exposure depend on factors such as:
For internal exposure, factors such as the physical and chemical properties of the radionuclide, activity, and biokinetics influence the level of exposure.
Each task in a nuclear medicine facility contributes to the external exposure of workers. These tasks include:
For staff working full time in nuclear medicine with optimized protection, the yearly effective dose should generally be well below 5 mSv.
The highest effective dose to workers typically comes from patients during injection and imaging procedures. For example, the dose rate near a patient who has received 350 MBq of 18F may be as high as 300 μSv/h at a distance of 0.5 meters.
High equivalent doses to the fingers can occur during the preparation and administration of radiopharmaceuticals, even with proper shielding. For instance, injecting eight patients per day with 400 MBq of 99mTc each has been reported to result in a mean equivalent dose to the fingers of 80 mSv/a, with a maximum dose of 330 mSv/a, even with syringe shields. Without shielding, the maximum dose could be as high as 2500 mSv/a.
Internal exposure risks arise from contamination, which may occur in various situations, including:
Traces of radionuclides can be found in numerous locations within the facility, such as on door handles, taps, equipment, and even in patient toilets. Whole body measurements of workers have revealed internal contamination levels of up to 10 kBq of 99mTc, which results in an effective dose of ~0.05 mSv/a.
Skin contamination is of particular concern, as it can lead to high local equivalent doses. For example, 1 kBq of 18F can result in an initial skin dose rate of 0.8 mSv/h. After handling 99mTc radiopharmaceuticals, activity levels on the hands can range from 0.02 to 200 kBq, leading to skin doses of 0.005–50 mSv/h.