What is the risk of cancer after a single Positron Emission Tomography (PET) scan?

Risk of Cancer from a Single PET Scan

The risk of cancer from a single PET scan is extremely low, with estimated lifetime attributable risk of cancer being approximately 0.1-0.2% for a typical adult patient. 1

Understanding PET Scan Radiation Exposure

PET scans involve two sources of radiation:

1. FDG (radioactive tracer): The injected radioactive glucose analog
2. CT component: When performed as part of PET/CT

Quantifying the Risk

The radiation exposure from a single PET/CT scan varies based on several factors:

• Patient age: Younger patients have higher lifetime risk
• Patient sex: Women generally have slightly higher risk than men
• Protocol used: Different CT protocols result in different radiation doses
• Body area scanned: Whole-body scans involve more radiation than limited scans

For context, a typical whole-body PET/CT scan delivers an effective dose of:

• 13-32 mSv depending on the CT protocol used 1
• This translates to approximately:
  • 0.16-0.32% lifetime attributable risk for a 20-year-old male
  • 0.23-0.51% lifetime attributable risk for a 20-year-old female
  • Significantly lower risk for older patients 1

Risk Factors That Modify Cancer Risk

The cancer risk from a PET scan is influenced by:

• Age: Risk decreases with increasing age at exposure 1
• Sex: Females generally have 20-30% higher risk than males 1
• Cumulative exposure: Multiple scans increase risk proportionally
• Protocol selection: Lower-dose CT protocols reduce risk

Putting the Risk in Perspective

For comparison:

• The lifetime attributable risk from annual CT scans of chest, abdomen, and pelvis for 10 years is estimated at 0.9% for men and 1.3% for women 2
• Annual PET/CT scans for 10 years carries an estimated lifetime risk of 1.6% for men and 1.9% for women 2

Clinical Recommendations

The American College of Radiology recommends:

1. PET/CT should only be performed when clinically justified 3
2. The benefits of accurate staging and diagnosis typically outweigh the small radiation risk 3
3. PET/CT should ideally be performed within 60 days of planned treatment 3
4. Measures should be taken to reduce radiation dose when possible 1

Special Considerations

• Pediatric and young adult patients: Higher lifetime risk due to greater tissue radiosensitivity and longer remaining lifespan 2
• Pregnant patients: PET scans are generally contraindicated unless absolutely necessary
• Patients requiring multiple scans: Consider cumulative exposure when planning surveillance protocols 4

The benefits of PET scanning for diagnosis, staging, and treatment planning in appropriate clinical scenarios far outweigh the small theoretical risk of radiation-induced malignancy for most patients.