Understanding Radiation in PET CT
A PET CT scan involves two sources of radiation: the radioactive tracer that is injected before the scan, and the X-rays used by the CT component. Both contribute to the total radiation dose you receive during the examination.
The combined dose from a typical PET CT scan is carefully controlled and falls within established medical guidelines. It is comparable to several years of natural background radiation (the low-level radiation everyone receives from the environment, the ground, and cosmic rays).
How Does It Compare to Other Sources?
To put the dose in perspective: everyone receives background radiation from natural sources, estimated at roughly 2 to 3 millisieverts (mSv) per year depending on where you live. A chest X-ray delivers approximately 0.02 mSv. A PET CT scan typically delivers somewhere in the range of 10 to 25 mSv, depending on the tracer used and the CT protocol.
While this is higher than a simple X-ray, it is within the range of other common medical imaging procedures such as a diagnostic CT scan of the abdomen. The dose is carefully justified by the clinical need: a PET CT scan provides information that simpler, lower-dose tests cannot.
How Quickly Does the Tracer Leave the Body?
The radioactive tracer used in PET CT has a short half-life, which means it loses its radioactivity relatively quickly. FDG, the most common tracer, has a half-life of about 110 minutes, meaning that after roughly 2 hours, half of the radioactivity has decayed. Within several hours, the tracer has largely cleared from the body through natural processes, primarily urination.
Drinking water after the scan helps flush the remaining tracer from your system faster. By the end of the day, the amount of radioactivity in your body is negligible.
Is It Safe for People Around Me?
After a PET CT scan, you emit a very small amount of radiation for a few hours as the tracer decays and clears from your body. As a general precaution, you may be advised to avoid prolonged close contact (sitting right next to for extended periods) with pregnant women and very young children for a few hours after the scan.
Casual contact, brief interactions, and normal daily activities are safe. The radiation levels are low and decrease rapidly with time and distance.
Pregnancy and Breastfeeding
PET CT scans are generally not performed on pregnant women unless the clinical need is urgent and no alternative is available. If you are pregnant, suspect you might be, or are breastfeeding, it is essential to inform the medical team before the scan. Special precautions or alternative imaging may be recommended.
For breastfeeding mothers, the nuclear medicine team will advise on whether a temporary interruption in breastfeeding is needed after the scan and for how long.
Balancing Risk and Benefit
Every medical procedure involves a balance between potential risks and expected benefits. For PET CT scans, the radiation dose is low and the risk of harm from a single scan is very small. The clinical information the scan provides, which can influence diagnosis, staging, and treatment decisions, typically outweighs this small risk by a significant margin.
If you have concerns about radiation exposure, particularly if you have had multiple scans, discuss them with your doctor. The medical team considers the cumulative radiation history when deciding whether additional imaging is needed and may choose alternative approaches when appropriate.