Definition – BED
A way to compare different fractionation regimens by normalizing the total biological effect.

Formula:
BED = nd [1 + d / (α/β)]

• n = number of fractions

• d = dose per fraction

Definition – EQD2
Equivalent dose in 2 Gy fractions:
EQD2 = BED / [1 + 2 / (α/β)]

Clinical importance

• Used for reirradiation and comparing protocols.

• Example: 60 Gy in 30 fractions (2 Gy/fx, α/β = 10):
  BED = 60 × [1 + 2/10] = 72 Gy₁₀.
  EQD2 = 60 Gy (same as given, since it’s already 2 Gy fractions).

• Example: 60 Gy in 20 fractions (3 Gy/fx, α/β = 10):
  BED = 60 × [1 + 3/10] = 78 Gy₁₀ → EQD2 = 65 Gy.