What is the linear no-threshold (LNT) model?

• A. Cancer risk increases with dose but is capped at high doses.
• B. Cancer risk is independent of dose.
• C. Cancer risk is zero below a threshold.
• D. Cancer risk increases linearly with dose with no safe threshold.

Answer: (D)

Linear no-threshold means that any amount of ionizing radiation adds some cancer risk, and that risk increases in direct proportion to the dose with no safe, zero-risk level. In other words, there is no dose small enough to be considered risk-free; the incremental risk scales with how much radiation you receive, and the total cancer risk from exposure equals the baseline lifetime risk plus a dose-proportional increment.

This is the description that matches the idea that risk grows linearly without a safe threshold, which is why it’s the best fit. Other statements describe risk that plateaus at high doses, or is independent of dose, or is zero below a certain dose—none of those align with the linear no-threshold concept. In practice, LNT is used in radiation protection to provide a conservative estimate of risk at low doses by extrapolating from higher-dose data.