Which factor describes the relative biological effectiveness of different radiations?

• A. Relative biological effectiveness (RBE)
• B. Radiation weighting factor (Wr)
• C. Linear energy transfer (LET)
• D. Tissue weighting factor (Wt)

Answer: (A)

Relative biological effectiveness describes how different radiations compare in their biological impact for the same absorbed dose. It is defined as the dose of a reference radiation needed to produce a given biological effect, divided by the dose of the test radiation needed to produce the same effect. This ratio captures why the same physical dose from different radiations can cause different levels of damage, and it depends on the biological endpoint and irradiation conditions. So, the factor that describes the relative biological effectiveness of different radiations is RBE.

Other terms have different roles: linear energy transfer describes how energy is deposited along the radiation track; radiation weighting factor and tissue weighting factor are used to translate absorbed dose into protective or risk-related quantities, not to directly compare biological effectiveness. High-LET radiations, like alpha particles, typically have higher RBE than low-LET radiations such as X-rays, reflecting denser ionization and more biological damage per unit dose.