Stochastic vs Non-Stochastic Effects

I was asked a question about the difference between stochastic and non-stochastic effects of radiation, and I decided to make my answer public.

Everyone is concerned about how radiation dose affects their body. The way the human body responds to radiation dose (dose-response) is classified into two broad categories of health effects: stochastic and non-stochastic. Non-stochastic is also called deterministic.

Stochastic Effects
Stochastic effects are typically associated with long-term, low-level (chronic) exposure to radiation. The word "Stochastic" refers to the likelihood or probability that an effect will happen. In the diagnostic range of x-radiation that Radiographers and the general public are exposed to, increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.

The primary stochastic effects are: Cancer and genetic defects.

Cancer is considered by most people as the primary health effect from radiation exposure.

Radiation can also cause changes in DNA, the "blueprints" that ensure cell repair and replacement. Changes in DNA are called mutations.

Sometimes the body fails to repair these mutations or even creates mutations during repair. The mutations can be teratogenic or genetic. Teratogenic mutations are caused by exposure of the fetus in the uterus and affect only the individual who was exposed. Genetic mutations are passed on to offspring.

In summary, Stochastic effects are:

*totally random (occur by chance)

*appear in non-exposed persons as well as exposed persons

*No Threshold--any dose can cause an effect

*the likelihood of an effect increases as the radiation dose increases, but a single photon can cause an effect

*the severity of the response is independent of the dose (the severity of cancer is not associated with the amount of dose received. You are more likely to get cancer if you receive a higher dose, but the severity of the disease is not based on the dose)

Non-Stochastic (Deterministic) Effects

Non-stochastic effects are those in which the severity of the effect varies with the dose and for which a threshold value exists.

Non-stochastic effects appear in cases of exposure to high levels of radiation, and become more severe as the exposure increases. Short-term, high-level exposure is referred to as 'acute' exposure.

Many non-cancerous health effects of radiation are non-stochastic.

Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness.

Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function.

Summary of non-stochastic effects:

*Threshold--A certain minimum dose must be exceeded before the particular effect is observed. Because of this minimum dose, the non-stochastic effects are also called Threshold Effects. The threshold may differ from individual to individual

*The severity of the effect increases with the size of the dose received by the individual. (More dose more severe effect)*There is a clear relationship between exposure to radiation and the observed effect on the individual.

Examples of Non-Stochastic effects: