BED Calculator

What Is Biologically Effective Dose?

Biologically effective dose (BED) quantifies the biological impact of radiotherapy by accounting for fraction size and tissue radiosensitivity. EQD₂ converts any fractionation scheme into an equivalent total dose delivered in 2 Gy fractions. Related: Radiation Converter.

BED and EQD₂ Formulas

Total dose = dose per fraction × number of fractions.

$$\text{BED} = \text{total dose} \times \left(1 + \frac{d}{\alpha/\beta}\right)$$

$$\text{EQD}_2 = \text{total dose} \times \frac{d + \alpha/\beta}{2 + \alpha/\beta}$$

Here $d$ is the dose per fraction in Gy and $\alpha/\beta$ is the tissue-specific ratio in Gy. Early reacting tissue typically uses $\alpha/\beta \approx 10$; late reacting tissue uses about 3; CNS and kidney about 2.