# Biologically effective dose (BED) and EQD2

Source: https://onco.cc/terms/biologically-effective-dose/  
OnCo record `biologically-effective-dose` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A way of converting any radiotherapy schedule into a common currency so that, say, five big doses can be compared with 25 small ones. EQD2 expresses the same thing as the equivalent total dose in 2 Gy fractions.

## Summary

Because the effect of radiation depends on fraction size as well as total dose, physicists calculate the biologically effective dose from the total dose, the dose per fraction and the tissue's alpha/beta ratio. EQD2 rescales this to the dose that would have the same effect if given in 2 Gy fractions, the historical standard. Both are used to design hypofractionated schedules, sum doses in re-irradiation and compare brachytherapy with external beam.

## Fields

- Kind: Term
- Last checked: 2026-09-16
- Tags: radiation-wave1

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Linear-quadratic_model
- Wikipedia: https://en.wikipedia.org/wiki/Linear-quadratic_model

## Connected records

- technologies: [High-dose-rate brachytherapy](https://onco.cc/technologies/hdr-brachytherapy/), [Hypofractionated radiotherapy](https://onco.cc/technologies/hypofractionated-radiotherapy/), [The linear-quadratic model and fractionation](https://onco.cc/technologies/linear-quadratic-model/)
- terms: [Re-irradiation](https://onco.cc/terms/re-irradiation/)

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