Clonogenic Survival

The colony-formation assay measures whether a treated cell retains the capacity to divide indefinitely. Counting colonies is only half the job - you have to correct for plating efficiency before a surviving fraction means anything. Gradiance does the correction and fits the survival curve.

What it measures

• Plating efficiency. The fraction of untreated cells that form colonies - the baseline every other condition is normalized against.
• Surviving fraction. Colonies formed relative to cells seeded, corrected for plating efficiency, at each dose.
• Radiosensitivity. When doses are radiation, the linear-quadratic parameters α and β, and survival at reference doses.

Data you upload

• Colony counts per well or dish, with the number of cells seeded.
• The dose (drug concentration or radiation dose) for each condition, including the zero-dose control.

What you get back

• Plating efficiency for the control.
• Corrected surviving fraction at each dose, with error bars.
• A survival curve on a log scale; for radiation, the linear-quadratic fit with α, β, and the α/β ratio.

Method note

Surviving fraction is colonies counted divided by (cells seeded × plating efficiency), so the untreated control sets the denominator for everything else. Radiation survival is fit to the linear-quadratic model S = exp(−αD − βD²) on a log-survival axis, the standard model in radiobiology; the α/β ratio summarizes how the curve bends and is reported directly.

Related

For graded viability dose-response (rather than colony counts), see Dose-Response and Cell-based Assays. For time-to-event survival curves, see Survival Analysis.