# Alpha/beta ratio

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

## TL;DR

A number for each tissue or tumour that says how much it cares about the size of each radiation dose. Low (around 2 to 3): very sensitive to big fractions, like the spinal cord and prostate cancer. High (around 10): mostly cares about total dose, like most tumours.

## Summary

In the linear-quadratic model the alpha/beta ratio is the dose at which the linear and quadratic parts of cell killing are equal. Late-responding normal tissues and a few tumours (prostate, breast) have low ratios, so large fractions hurt or help them disproportionately; most tumours and acutely reacting tissues have high ratios. The ratio explains why hypofractionation is safe and effective in breast and prostate cancer and why the spinal cord is spared by small fractions.

## Fields

- Kind: Term
- Last checked: 2026-09-17
- Also known as: alpha/beta; α/β; alpha-beta ratio; a/b ratio; alpha beta
- Tags: radiation-wave1

## Sources

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

## Connected records

- terms: [Alpha vs beta emitters](https://onco.cc/terms/alpha-vs-beta/), [Linear energy transfer (LET)](https://onco.cc/terms/linear-energy-transfer/), [Relative biological effectiveness (RBE)](https://onco.cc/terms/relative-biological-effectiveness/)
- technologies: [Carbon-ion therapy](https://onco.cc/technologies/carbon-ion/), [Hypofractionated radiotherapy](https://onco.cc/technologies/hypofractionated-radiotherapy/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Proton therapy](https://onco.cc/technologies/proton-therapy/), [Radiogenomics: predicting radiation sensitivity from genes](https://onco.cc/technologies/radiogenomics/), [The linear-quadratic model and fractionation](https://onco.cc/technologies/linear-quadratic-model/)
- trials: [CHHiP](https://onco.cc/trials/chhip/), [FAST (5-fraction whole-breast radiotherapy)](https://onco.cc/trials/fast-trial/), [PARTIQoL](https://onco.cc/trials/partiqol/), [START-A (UK Standardisation of Breast Radiotherapy, trial A)](https://onco.cc/trials/start-a/), [START-B (UK Standardisation of Breast Radiotherapy)](https://onco.cc/trials/start-b/)
- pairings: [Caution: proton therapy vs IMRT](https://onco.cc/pairings/proton-vs-imrt/)
- ideas: [Pooled coverage-with-evidence for proton therapy across all centres](https://onco.cc/ideas/idea-fund-proton-coverage-with-evidence/), [Use LET, RBE and alpha/beta to decide when protons beat IMRT](https://onco.cc/ideas/idea-bio2-let-rbe-ab-selects-protons/)
- key papers: [Paganetti 2014: proton RBE is not a fixed 1.1](https://onco.cc/key-papers/paper-paganetti-proton-rbe-ijrobp-2014/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/)

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