Effective dose: practice, purpose and pitfalls for nuclear medicine

Area of Science:

• Medical Physics
• Radiological Protection
• Nuclear Medicine

Background:

• Effective dose (E) is a practical quantity for assessing stochastic health detriment from ionizing radiation.
• E is widely used in medical exposures for comparing doses across different examinations and sources.
• The International Commission on Radiological Protection (ICRP) developed E for radiation protection calculations.

Purpose of the Study:

• To analyze potential uncertainties in effective dose (E) for nuclear medicine examinations.
• To enable users to judge the reliability of E as a comparator of relative risk in nuclear medicine.
• To address the tendency to over-attribute accuracy to E values in medical exposures.

Main Methods:

• Analysis of component parts of effective dose (E) based on their considered accuracy.
• Assessment of uncertainties in E for various nuclear medicine procedures.
• Comparison of uncertainties between nuclear medicine and radiology procedures.

Main Results:

• Uncertainties in effective dose (E) for nuclear medicine procedures are approximately ±50%.
• These uncertainties are larger than for radiology due to substantial contributions from single organ doses, particularly the bladder.
• A 2007 revision of tissue weighting factors resulted in a 10% decrease in mean E for nuclear medicine.

Conclusions:

• Effective dose (E) is a valuable tool for justifying nuclear medicine examinations but has significant limitations.
• Physicians must be aware of the ±50% uncertainty in E when communicating radiation risks to patients.
• Cancer risk estimations based on E can vary by one to two orders of magnitude, necessitating clear communication of risk.