# Relative biological efficiency

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## Relative biological efficiency (RBE)

To describe the differences in cell or tissue response between gamma or x-ray radiation and heavy charged particle beam, the RBE has been introduced:

$RBE = \frac{D_{endpoint}(HCP radiation)}{D_{endpoint}(X rays)}$

The RBE is dependent on many factors such as the system investigated (cell line etc.), the chosen biological endpoint, the physical dose, the LET etc.

Amorphous track models can be used to predict the RBE from physical beam parameters (fluences, particle types and energy spectra) and the photon response of a system.