American Registry of Radiologic Technologists (ARRT) Practice Exam

If the dose-response curve begins at zero, what does this imply?

1. There is a threshold

2. There is no threshold

3. There is a safety limit

4. There is a linear response

The correct answer is: There is no threshold

If the dose-response curve begins at zero, this implies that there is no threshold. In a dose-response relationship, a threshold represents a specific level of exposure below which no effect is expected. When the curve starts at zero, it suggests that even the smallest dose can produce a measurable biological effect. This indicates that every increment in dose continuously contributes to the observable effect, thereby confirming the absence of a threshold level within that range. Understanding this concept is critical in fields such as radiology and toxicology because it impacts how practitioners interpret the potential risks of exposure to radiation or other hazardous substances. A dose-response curve starting at zero often means that even minimal exposures should be minimized or controlled, emphasizing safety and the importance of risk assessment in radiologic practices.