# Quality factor

A dimensionless factor defined to reflect the relative biological effectiveness of high-LET radiations compared with low-LET radiations at low exposure levels. [math]Q[/math] is usually given by a function [math]Q(L)[/math], where [math]L[/math] is the unrestricted LET in water. The quality factor at a point in tissue, is given by:

[math] Q = \frac{1}{D} \int_{L=0}^\infty Q(L)D_LdL [/math]

where [math]D[/math] is the absorbed dose at that point, [math]D_L[/math] is the distribution of [math]D[/math] in unrestricted LET [math]L[/math] at the point of interest, and [math]Q(L)[/math] is the quality factor as a function of [math]L[/math]. The integration is to be performed over [math]D_L[/math], due to all charged particles, excluding their secondary electrons.

ICRP Publication 116, 2010 and ICRP Publication 123, 2013

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## Previous glossary entries

### from ICRP Publication 103, 2007 and ICRP Publication 127, 2014

The factor characterising the biological effectiveness of a radiation, based on the ionisation density along the tracks of charged particles in tissue. [math]Q[/math] is defined as a function of the unrestricted linear energy transfer, [math]L_\infty[/math] (often denoted as [math]L[/math] or LET), of charged particles in water:

[math] Q(L) = \begin{cases} 1, & \text{if } L \lt \text{10 keV/μm} \\ 0.32L - 2.2, & \text{if 10} \le L \le \text{100 keV/μm} \\ 300/\sqrt{L}, & \text {if } L \gt \text{100 keV/μm} \end{cases} [/math]

[math]Q[/math] has been superseded by the radiation weighting factor in the definition of equivalent dose, but it is still used in calculating the operational dose equivalent quantities used in monitoring.