The linear-quadratic model explains why the same total dose has different effects when given in fewer, larger fractions. BED and EQD2 let radiation oncologists compare conventional, hypofractionated and stereotactic schedules.
How to use the BED and EQD2 Calculator
- Number of fractions
- Dose per fraction
- α/β ratio
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the number of fractions, the dose per fraction and the α/β ratio.
Tips
- Keep a record of your imaging and its doses.
- Ask whether an ultrasound or MRI could answer the question without radiation.
- Tell staff if you might be pregnant.
- Background radiation varies by altitude and region.
Common mistakes to avoid
- Comparing mSv (effective dose) with mGy (absorbed dose).
- Assuming every scan of the same type gives the same dose.
- Ignoring cumulative dose from repeated scans.
Inputs explained
| Field | What to enter |
|---|---|
| Number of fractions | A number |
| Dose per fraction | In Gy |
| α/β ratio | In Gy |
What each result means
- Total physical dose = [Number of fractions]×[Dose per fraction]
- Biologically effective dose = [Number of fractions]×[Dose per fraction]×(1 + [Dose per fraction]÷[α÷β ratio])
- EQD2 = [Biologically effective dose]÷(1 + 2÷[α÷β ratio])
- BED for late tissues (α/β 3) = [Number of fractions]×[Dose per fraction]×(1 + [Dose per fraction]÷3)
Example values
How the main result changes when Number of fractions changes and everything else stays at the example values above:
| Number of fractions | Biologically effective dose (Gy) |
|---|---|
| 10 | 35.1 |
| 15 | 52.6 |
| 20 | 70.1 |
| 25 | 87.7 |
| 30 | 105.2 |
| 40 | 140.3 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
BED = n × d × (1 + d ÷ (α/β))
EQD2 = BED ÷ (1 + 2 ÷ (α/β))
α/β ≈ 10 Gy for tumours and early-reacting tissues, ≈ 3 Gy for late-reacting tissues (≈ 1.5 for prostate cancer)
Worked example
Inputs — Number of fractions: 20; Dose per fraction: 2.75 Gy; α/β ratio: 10 Gy.
Results — Total physical dose = 55 Gy; Biologically effective dose = 70.1 Gy; EQD2 = 58.4 Gy; BED for late tissues (α/β 3) = 105.4 Gy.
Key terms
- BED
- Biologically effective dose.
- EQD2
- Equivalent dose in 2 Gy fractions.
Frequently asked questions
What is EQD2?
The dose in 2 Gy fractions that would have the same biological effect.
Why does α/β matter?
Tissues with low α/β are more sensitive to large fractions.
Does BED account for treatment time?
Not in this basic form; repopulation corrections exist for long treatments.