A biologic reaction is produced by 4 Gyt of a test radiation. It takes 16 Gyt of 250-kVp x-rays to produce the same biologic reaction. What is the relative biologic effectiveness (RBE) of the test radiation

4

Explanation:

Relative Biological Effectiveness (RBE) =

Standard Radiation dose / Test Radiation dose

for achieving the same biological effect.

The absorbed radiation dose is measured in units of Gyt (Gray in tissue).

In the given scenario, Standard radiation dose of 250 KVp X-rays = 16 Gyt

Corresponding Test Radiation dose = 4 Gyt

Therefore, Relative Biological Effectiveness = 16/4 = 4