# Bragg peak

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

## TL;DR

The spot where a proton or carbon-ion beam dumps most of its energy and then stops, so tissue behind the tumour gets almost no dose.

## Summary

A charged particle slows as it travels through tissue and deposits most of its energy in a narrow peak just before it stops. That Bragg peak is why protons and carbon ions have no exit dose compared with X-rays. The spread-out Bragg peak stacks several energies to cover a tumour's depth. Linear energy transfer, and therefore relative biological effectiveness, is highest at the distal edge of the peak, which is why a constant proton RBE of 1.1 can understate dose just beyond the target. Range uncertainty of a few millimetres is the planning counterpart of that edge.

## Fields

- Kind: Term
- Last checked: 2026-09-17
- Also known as: Bragg peak; spread-out Bragg peak; SOBP; distal edge; no exit dose
- Tags: radiation-wave5

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Bragg_peak
- Wikipedia: https://en.wikipedia.org/wiki/Bragg_peak

## Connected records

- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/)
- technologies: [Carbon-ion therapy](https://onco.cc/technologies/carbon-ion/), [Pencil-beam scanning and intensity-modulated proton therapy](https://onco.cc/technologies/intensity-modulated-proton-therapy/), [Proton arc therapy](https://onco.cc/technologies/proton-arc-therapy/), [Proton therapy](https://onco.cc/technologies/proton-therapy/)
- terms: [Linear energy transfer (LET)](https://onco.cc/terms/linear-energy-transfer/), [Relative biological effectiveness (RBE)](https://onco.cc/terms/relative-biological-effectiveness/)
- pairings: [Caution: proton therapy vs IMRT](https://onco.cc/pairings/proton-vs-imrt/)
- ideas: [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/)
- trials: [PARTIQoL](https://onco.cc/trials/partiqol/), [RADCOMP](https://onco.cc/trials/radcomp/)

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JSON: https://onco.cc/api/v1/entities/bragg-peak.json