TOPIC 7: Causes of Dose

Let’s explore Causes of Dose.

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Stochastic effects are those that occur on a random basis, their effect being independent of the dose.  The effect typically has no threshold and is based on probabilities, with the chances of seeing the effect increasing with increasing exposure.  Some cancers are thought to be a stochastic effect of radiation.  An example of a stochastic effect is buying a lottery ticket.  Buy one ticket and there is a chance it could be a winner – but it is not guaranteed.  Buy more tickets and the odds of winning increase.

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Non-stochastic effects are those that can be related directly to a radiation dose received –  the higher the dose – the more severe the effect.  For instance, spending the day outside, in the bright sun is an example of a non-stochastic effect of non-ionizing radiation.  The more time in the sun, the more intense the sunburn.  In effect, the burn gets worse as the dose increases.  Typically, there is a threshold, below which an effect will not occur.  This is the result of the body being able to heal itself from minor insults and injuries.

Non-stochastic effects are also called deterministic effects. Skin burns and cataracts are non-stochastic effects of radiation.  Patients receiving radiation therapy for treatments to cancers may show non-stochastic effects manifested as some degree of radiation sickness, such as nausea or diarrhea.