From the Guidelines
A PET scan typically delivers more radiation than a CT scan, with the radiation dose ranging from 7-25 millisieverts (mSv) for a PET scan, compared to 2-10 mSv for a standard CT scan, as reported in the most recent study 1.
Radiation Exposure Comparison
The higher radiation dose in PET scans comes from two sources: the injected radioactive tracer (commonly F-18 FDG) and the CT component that is often performed as part of a combined PET/CT scan for anatomical correlation.
- The radioactive tracers used in PET imaging emit positrons that produce gamma rays, contributing significantly to the overall radiation exposure.
- The CT component of a PET/CT scan can also contribute to the overall radiation dose, with the effective CT dose ranging from 1 to 20 mSv, depending on the intended use of the CT study and the specific protocol used 1.
Factors Influencing Radiation Exposure
The radiation exposure from a PET/CT scan depends on several factors, including:
- The specific protocol and radiopharmaceutical used
- The age and weight of the patient
- The body region being imaged
- The type of CT scan used (e.g. low-dose, diagnostic, or high-resolution)
Clinical Considerations
Despite the higher radiation dose, PET scans provide unique metabolic and functional information that cannot be obtained from CT scans alone, which primarily show anatomical structures.
- The radiation risk must be weighed against the valuable diagnostic information these scans provide, and physicians typically order these tests only when the potential benefits outweigh the radiation exposure risks 1.
- The ALARA principle (As Low As Reasonably Achievable) should always be considered, and efforts should be made to optimize CT protocols and reduce radiation exposure, particularly in pediatric patients 1.
From the Research
Radiation Exposure Comparison
- A PET scan and a CT scan are both used in medical imaging, but they have different radiation exposure levels.
- According to the study 2, the average radiation dose for the PET component is 8.19 ± 0.83 mSv, while the CT component has an average radiation dose of 13.44 ± 5.14 mSv.
- The study 3 also mentions that the CT dose component is often higher in magnitude than the dose from PET alone.
Factors Affecting Radiation Exposure
- The study 3 suggests that factors such as proper justification for ordering contrast-enhanced CT, use of automatic exposure control features, and optimisation of scan parameters can help reduce the patient's dose from CT alone.
- The study 4 notes that the total effective dose to the patient from a PET/CT procedure is approximately 10 mSv, with the major part coming from internal irradiation due to radiopharmaceuticals and a minor part from the CT scan.
- The study 5 investigates the use of ultra-low dose CT scanning for PET/CT and finds that introducing a tin (Sn) filter in CT imaging can lower radiation dose by more than 90% with minimal effect on PET image quantification.
Cumulative Radiation Doses
- The study 6 discusses the concerns about cumulative radiation doses from repeated PET-CT examinations and suggests that implementation of justification for PET-CT examinations and utilisation of dose reduction measures are key issues in coping with the cumulative dose in patients.
- The study 2 also mentions that reducing the diagnostic area of the DCT scans and decreasing the use of certain DCT protocols can help decrease the effective radiation doses of PET/CT scans 2, 3.