Identify all true statements concerning biological effects.

• A. Stochastic effects assumes no threshold for risk from exposure
• B. Non-Stochastic effects assumes a threshold for risk from exposure
• C. Both statements are true
• D. Neither statement is true

Answer: (C)

Stochastic versus deterministic effects describe how radiation risk relates to dose. Stochastic effects, such as cancer or genetic effects, are modeled as having no true dose threshold—the probability of occurrence increases with dose, but there isn’t a specific dose below which nothing happens. Deterministic (non-stochastic) effects have a threshold: below that dose, no effect occurs, and above it the likelihood and severity of effects increase with dose. With that in mind, the first statement is correct about stochastic effects having no threshold, and the second statement is correct about non-stochastic effects having a threshold. Therefore, both statements are true.