How Long is a Patient Radioactive After PET CT
Patients remain radioactive for approximately 24 hours after a PET CT scan using FDG, with radiation levels decreasing significantly after the first few hours.
Radioactivity Duration and Safety Considerations
The radioactivity from a PET CT scan primarily comes from the injected radiopharmaceutical, typically 18F-FDG (fluorodeoxyglucose), which has a physical half-life of 110 minutes. This means:
- The radioactivity level decreases by 50% approximately every 2 hours
- Most of the radioactivity is eliminated from the body within 6-12 hours
- After 24 hours, the radiation level is considered negligible for practical purposes
Radiation Exposure Measurements
Research has shown that radiation dose rates from patients decrease rapidly after injection:
- Immediately after injection: highest radiation levels
- At 2 hours post-injection: moderate radiation levels
- At 4-6 hours post-injection: significantly reduced radiation levels 1
- After 24 hours: negligible radiation levels
Patient Instructions and Precautions
Based on the decreasing radiation levels, patients should follow these precautions:
First 6 Hours After Scan:
- Maintain distance from pregnant women and young children
- Limit close contact with others when possible
- Drink plenty of fluids to help eliminate the radiotracer through urine
- Use separate bathroom facilities if possible, and flush twice after use
6-24 Hours After Scan:
- Normal contact with adults is generally safe
- Continue to limit prolonged close contact with pregnant women and children
- Continue hydration to facilitate radiotracer elimination
Special Considerations
For Healthcare Workers:
Healthcare personnel working with PET/CT patients receive minimal radiation exposure when following standard protocols. The average dose received by staff has been calculated between 0.002-0.004 mSv per patient 1.
For Companions and Family Members:
- Companions may be exposed to a dose between 0.024-0.048 mSv when using private transportation 4-6 hours after injection 1
- Close contact between the patient and small children should be avoided for a few hours after the administration of the radiopharmaceutical 2
For Breastfeeding Mothers:
An interruption in breastfeeding is not necessary after a PET/CT procedure 2, though some centers may recommend a 6-hour pause as a precautionary measure.
Factors Affecting Radiation Duration
Several factors can influence how long a patient remains radioactive:
- Administered dose of the radiopharmaceutical
- Patient's hydration status and kidney function
- Patient's body mass
- Type of radiotracer used (though FDG is most common)
Conclusion
While patients are technically radioactive for about 24 hours after a PET CT scan, the radiation levels decrease rapidly due to the short half-life of 18F-FDG. Most radiation safety concerns are minimal after 6 hours, and patients can generally resume normal activities with minimal precautions after this time.