Radiation Risk Models Vocabulary

Key vocabulary terms and definitions related to radiation risk assessment models, including relative risk, absolute risk, and associated calculations.

Risk

Often expressed as the probability or likelihood that an event will occur.

Risk Assessment Models

There are two models used to assess the risk of stochastic effects from radiation exposure: relative risk and absolute risk.

Relative Risk

Multiplicative risk model.

Relative Risk

Computed by comparing the number of persons in the exposed population showing a given stochastic effect with the number in an unexposed population who show the same stochastic effect.

Relative Risk Rates

Range from 1 to 10, with 1 representing no risk at all.

Observed Late Effects in Humans (Relative Risk)

Most reports are in the range from 1 to 2.

BEIR Committee

Committee on the Biological Effects of Ionizing Radiation, associated with the National Academy of Sciences, used the relative risk model.

Relative Risk Calculation

Relative risk = Observed cases / Expected cases

Excess Relative Risk

Equal to the relative risk minus 1.

Excess Relative Risk Calculation

Determined by subtracting one from the relative risk calculated.

Absolute Risk

Additive risk model.

Absolute Risk

Predicts that a specific number of excess cancers will occur as a result of exposure.

Absolute Risk

States risk in terms of number of cases/106 persons/rad/year.

Absolute Risk

Assumes a linear dose-response relationship.

Excess Risk

Observed cases minus expected cases.

Excess Absolute Risk (EAR)

Also known as excess attributable risk.

Excess Absolute Risk (EAR)

Equal to the rate of disease in exposed population minus the rate of disease in unexposed population.

Excess Absolute Risk (EAR)

Difference between two absolute risk and is commonly used in radiation epidemiology expressed as the __ per unit dose.

Stochastic Effect

It is a chance occurrence and may not occur

Absolute Risk (example)

Absolute risk for radiation-induced breast cancer is presumed to be 6 cases/106 persons/rad/year at a 15-year at risk period.

Absolute Risk (example)

Absolute risk for radiation-induced breast cancer is presumed to be 12 cases/106 persons/rad/year at a 30-year at risk period.

Relative Risk Model

Incidence in exposed population - spontaneous incidence (unexposed)

Absolute Risk Model

radiation exposure (latency) X+c

Relative Risk

A measure of how much a particular factor affects the risk of a specific outcome

Excess Risk

The observed number of cases of a disease exceeds the expected number of cases.

EAR (Excess Absolute Risk)

The rate of disease in exposed population minus the rate of disease in unexposed population.

Committee Reports

BEIR VII and ICRP 103 state risk from radiation exposure as either absolute risk or relative risk.

Risk

refers to the potential harm, damage, or loss that may occur as a result of radiation exposure.

Relative Risk Model

Based on comparing disease incidence in exposed versus unexposed populations.

Absolute Risk Model

Models excess cancers as a specific number of cases per unit dose.

Observed Cases

Actual number of incidents or occurrences noted in a study.

Expected Cases

Number of occurrences anticipated under normal circumstances or in an unexposed group.

ERR (Excess Relative Risk)

Increase in risk above the baseline due to exposure.

Linear Dose-Response

Assumption that risk increases proportionally with dose.

Stochastic Effects

Effects whose probability is dose-dependent without threshold.

Risk Assessment

Evaluation of potential detrimental outcomes from radiation.

Unexposed population

A group not subjected to the radiation being studied.

Natural absolute risk

The rate of disease incidence without radiation exposure.

Exposed population

Group that has been subjected to the radiation being studied.

EAR per unit dose

Excess absolute risk adjusted to the quantity of radiation received.

Spontaneous incidence

Occurrence of a disease without a known cause.

Radiogenic excess

Increase in disease cases attributed to radiation.

Multiplicative risk model

Another Term for Relative Risk.

Additive risk model

Another term for absolute risk.

Biological Effects of Ionizing Radiations (BEIR)

A Committee whose reports express risk from radiation exposure.

International Commission on Radiological Protection (ICRP)

A Committee whose reports express risk from radiation exposure.

Excess cancers

Additional cancer cases caused by radiation exposure.

Disease cases

Instances of a particular illness or condition.

Natural absolute risk

A certain number of incidents of a disease in the general population.

Linear non- threshold (LNT) model

A risk model that suggests there is no safe dose of radiation.

Radiation exposure

Being subjected to ionizing radiation.

Dose-response relationship

Correlation between radiation dose and the risk of effects.

Epidemiology

The branch of medicine which deals with the incidence, distribution, and possible control of diseases and other factors relating to health.

Late effects

Damages or illnesses that occur long after initial radiation exposure.

Probability

The extent to which something is likely to occur.

Likelihood

The possibility of something happening.

Relative Risk Formula

Observed Rate / Expected Rate

Absolute Risk Formula

Cases per Population per Dose per Time

Excess Risk Formula

Observed Cases - Expected Cases

Excess Absolute Risk Formula

Exposed Rate - Unexposed Rate

Risk Management

The process of evaluating and mitigating radiation risks.

Medical Radiography

The imaging of the body for diagnostic purposes using X-rays.

Radiation Epidemiology

The rate of disease in exposed population divided by the rate of disease in unexposed population.

Threshold Dose

A certain radiation dose has to be reached before effects are seen.