BED / EQD2 Calculator
Biologically Effective Dose and Equivalent Dose in 2 Gy fractions for radiotherapy.
Calculator
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Why use it
Enables meaningful comparison of hypofractionated, hyperfractionated, and standard regimens. Essential for SBRT/SABR dose prescription and reporting.
About
Calculates the Biologically Effective Dose (BED) and Equivalent Dose in 2 Gy fractions (EQD2) using the Linear-Quadratic (LQ) model. Allows comparison of different radiotherapy fractionation schedules.
When to use
- Comparing different radiotherapy fractionation schedules
- Converting SBRT/SABR doses to EQD2 for toxicity modeling
- Designing altered fractionation regimens
- Literature comparison and trial interpretation
Formula
BED = D × (1 + d / (α/β))
EQD2 = D × (d + α/β) / (2 + α/β)
D = total dose (Gy), d = dose per fraction (Gy), n = number of fractions
Pearls & pitfalls
- α/β = 10 Gy: most tumors, acute-responding tissues (mucosa).
- α/β = 3 Gy: late-responding tissues (spinal cord, brain, rectum, bladder).
- α/β = 1.5 Gy: prostate cancer (evidence of low α/β).
- BED and EQD2 assume LQ model — may overestimate efficacy at very high doses/fraction (>8-10 Gy).
- EQD2 = BED / (1 + 2/[α/β])
Next steps
Use EQD2 for comparing schedules in terms of tumor control and normal tissue toxicity. Standard α/β = 10 Gy for tumors (fast-proliferating); α/β = 3 Gy for late-responding tissues (spinal cord, rectum).
Evidence
Fowler JF. The linear-quadratic formula and progress in fractionated radiotherapy. Br J Radiol. 1989;62:679-694.