Effective dose

Effective dose is a measure of the overall risk of health effects from ionizing radiation. It is defined as the sum of the equivalent doses to all body tissues, each multiplied by a weighting factor that reflects the sensitivity of that tissue to radiation. The unit of effective dose is the sievert (Sv).

Definition

The International Commission on Radiological Protection (ICRP) defines the effective dose (E) as the sum of the equivalent doses to all body tissues (HT), each multiplied by a tissue weighting factor (WT) that reflects the sensitivity of that tissue to radiation. The formula is:

E = Σ WT HT

The unit of effective dose is the sievert (Sv), which is equivalent to one joule per kilogram.

Tissue weighting factors

The ICRP has assigned tissue weighting factors to various body tissues based on their sensitivity to radiation. The most sensitive tissues, such as the bone marrow and the lungs, have the highest weighting factors. The sum of all tissue weighting factors is 1.

Equivalent dose

The equivalent dose (HT) to a tissue is the absorbed dose (D) multiplied by a radiation weighting factor (WR) that reflects the biological effectiveness of the type of radiation. The formula is:

HT = WR D

The unit of equivalent dose is also the sievert.

Uses

The effective dose is used to estimate the overall risk of health effects from exposure to ionizing radiation. It is used in radiation protection to set dose limits for workers and the public, and in radiation therapy to plan treatments.

Limitations

The effective dose is a simplified measure that does not take into account individual variations in sensitivity to radiation, or the actual distribution of dose within a tissue. It is intended for use in large populations and not for predicting health effects in individuals.

See also

• Absorbed dose
• Equivalent dose
• Radiation protection
• Radiation therapy