The alpha/beta ratio used in BED calculations reflects tissue sensitivity to fractionation. Which statement is true?

• A. Time to progression
• B. Alpha/beta ratio
• C. Tumor grade
• D. Patient age

Answer: (B)

The main idea is how tissue response changes with the size of each radiation fraction, which is captured by the alpha/beta ratio in the linear-quadratic model. The alpha/beta ratio is a radiobiological parameter that quantifies sensitivity to fractionation: tissues with a high value (around 10 Gy) are less influenced by how the dose is split into fractions, while those with a low value (around 3 Gy or lower) show a much greater change in effect with different fraction sizes. This is exactly why BED calculations use this ratio: BED = nd [1 + d/(α/β)], so the ratio controls how much the biological effect shifts when you alter the number of fractions or the dose per fraction. Hence, describing tissue sensitivity to fractionation with the alpha/beta ratio is the correct framing. Other factors like time to progression, tumor grade, or patient age don’t quantify this radiobiological sensitivity to fractionation and don’t enter the BED calculation in the same way.