Radiotherapy planning
Biologically Effective Dose (BED)
The linear-quadratic model approximates radiobiologic effect of different fractionation schemes. Adjust the α/β ratio for target tissues (tumor vs. late-responding organs) to compare regimens.
Typical: tumors (≈10 Gy), late-responding normal tissue (≈3 Gy).
Set to 10 Gy for tumor EQD2, 3 Gy for late tissue comparison.
Total physical dose
54.0 Gy
n × d
BED
63.7 Gy
BED = nd × (1 + d ÷ α/β)
EQD2
53.1 Gy
EQD2 (α/β = 10): 53.1 Gy
Characteristic of hypofractionated palliation or low α/β tissues. Ensure clinical goal aligns with dose intensity.
How to Use This Calculator
Enter fractionation details
Provide number of fractions and dose per fraction from the planned regimen.
Select appropriate α/β ratio
Use tumor α/β for tumor control comparisons and late-responding α/β for organ-at-risk assessment.
Review BED and EQD2
Compare values with protocol standards, dose constraints, and historical regimens to ensure biological equivalence.
Formula
BED = n × d × (1 + d ÷ (α/β))
EQD2 = BED ÷ (1 + 2 ÷ (α/β))
n = number of fractions, d = dose per fraction (Gy), α/β = tissue-specific radiosensitivity (Gy).
Full Description
The biologically effective dose translates physical dose and fractionation into a biologic metric using the linear-quadratic model. It assists in comparing hypofractionated regimens with conventional schedules and evaluating cumulative dose to normal tissues. BED and EQD2 are foundational in stereotactic body radiotherapy, brachytherapy boosts, and retreatment planning.
While BED offers valuable insight, clinicians must also consider total treatment time, repopulation, organ motion, and patient-specific tolerance. Always correlate with modern planning constraints and peer-reviewed protocols.
Frequently Asked Questions
What α/β should I use?
Common choices: 10 Gy for many tumors, 3 Gy for late-responding normal tissues (spinal cord, rectum). Check literature for site-specific values.
Does BED account for overall treatment time?
Standard BED does not include time corrections. To model repopulation, extend the formula with kick-off time and dose-rate adjustments.
Can BED be negative?
No. Negative BED would imply biologic sparing. If calculations show negatives, recheck inputs and α/β assumptions.
Is EQD2 interchangeable between tissues?
EQD2 depends on α/β. Use the appropriate α/β for the tissue of interest to compare regimens accurately.