What are the risks and precautions associated with Positron Emission Tomography (PET) Computed Tomography (CT) scan radiation?

Radiation Risks and Precautions for PET/CT Scans

PET/CT scans expose patients to a total effective radiation dose of approximately 10 mSv, with the majority (6-7 mSv) coming from the radiopharmaceutical (typically FDG) and the remainder (2-4 mSv) from the CT component, though this can be significantly higher if a full diagnostic CT is performed 1.

Radiation Exposure Breakdown

Sources of Radiation in PET/CT

• PET component: 4-7 mSv from the radiopharmaceutical (typically 18F-FDG)
• CT component: 2-20+ mSv depending on protocol (low-dose vs diagnostic)
• Total effective dose: Typically around 10 mSv for a standard PET/CT scan 1

Comparison to Other Radiation Sources

• A standard PET/CT scan's radiation exposure is equivalent to approximately 3-5 years of natural background radiation
• The CT portion can be minimized through optimization techniques while maintaining diagnostic quality

Health Risks of PET/CT Radiation

Biological Effects

• PET/CT scanning can induce measurable DNA damage, with studies showing significant increases in chromosome aberrations post-scanning 2
• The stochastic risk (cancer induction) is the primary concern rather than deterministic effects
• Individual variation exists in radiation sensitivity and DNA repair capacity

Special Populations at Higher Risk

• Pregnant patients: PET/CT should be avoided or postponed unless vital for the patient 1
• Pediatric patients: Higher sensitivity to radiation effects due to:
  • More rapidly dividing cells
  • Longer life expectancy for radiation effects to manifest
  • Smaller body size leading to higher organ doses 3
• Patients requiring multiple scans: Cumulative exposure increases risk

Radiation Dose Reduction Strategies

Technical Optimization

• Ultra-low dose CT protocols: Using tin (Sn) filters can reduce CT radiation by more than 90% while maintaining adequate image quality for attenuation correction 4
• Tube current modulation: Adjusting mAs based on patient size and anatomy
• Limiting scan range: Scanning only the clinically relevant body regions 3
• Optimized reconstruction algorithms: Allow for dose reduction while maintaining image quality

Patient-Specific Approaches

• Weight-based radiopharmaceutical dosing: Typically 0.1 mCi/kg of FDG 3
• Proper patient positioning: Arms up when possible to reduce photon starvation artifacts and radiation dose 3
• Limiting scan range: Avoiding unnecessary imaging of areas not clinically indicated

Radiation Safety Precautions

For Patients

• Hydration: Adequate pre-hydration (approximately 1L of water) to reduce FDG concentration in urine and minimize radiation to the bladder 3, 5
• Voiding: Emptying the bladder immediately before scanning to reduce bladder radiation exposure 5
• Post-scan precautions:
  • No interruption in breastfeeding is necessary after PET/CT
  • Close contact with small children should be avoided for a few hours after the procedure 1

For Healthcare Workers and Public

• Distance: Maintain maximum practical distance from radioactive patients
• Time: Minimize time spent in close proximity to patients who have received radiopharmaceuticals
• Shielding: Use appropriate barriers when handling radiopharmaceuticals

Balancing Risks and Benefits

• The diagnostic information gained from PET/CT often outweighs the radiation risks for most patients
• The ALARA principle (As Low As Reasonably Achievable) should guide all PET/CT protocols
• Newer technologies continue to reduce required radiation doses while maintaining diagnostic quality

Future Directions in Radiation Dose Reduction

• Long axial field of view (LAFOV) PET scanners combined with ultra-low dose CT can significantly reduce overall radiation exposure 4
• Advanced reconstruction algorithms and artificial intelligence techniques are improving image quality at lower radiation doses
• Standardized dose reporting and tracking may help optimize protocols and monitor cumulative patient exposure

While PET/CT scans do involve radiation exposure, the clinical benefits typically outweigh the risks when the examination is properly indicated. Continued advances in technology are steadily reducing the radiation dose required while maintaining or improving diagnostic quality.