Question

Q1. Cell survival curves

Suppose you did an experiment to generate a cell survival curve.

a) Describe what steps you would take to do the experiment.

b) What is meant by plating efficiency?

c) In your experiment you irradiate cells using 6 MV photons on a linear accelerator. You collect the data shown in the table below. Plot cell survival as a function of dose and use the linear-quadratic model to fit the data.

d) Determine the alpha/beta ratio from the curve fit. Is this an early responding or late responding cell line?

Number of cells plated	Number of colonies counted	Dose (Gy)
100	75	0
400	255	2
400	180	5
1000	150	10
10000	90	20

Answer 1

A) You start by preparing the cells to either be the control group or be one of the treatment groups. You plate some cells for the control group and then you prepare some moer plates depending on the number of treatments you want to apply, that would be one plate for each radiation dose. Then you apply the treatments and count the surviving cells. Now you have the data to analyse, you may apply a chart and a linear quadratic model.

B) All the experiment depends on a good plating, if you do an efficient plating then you eliminate any other factor that may affect cell survival. Remember we want to measure the effect of the treatments, so we need to eliminate any other factor.

C) You just have to plot the data, but remember you have to calculate the percentage of surviving cells and use those percentages in the graph and not the colonies counted per se. This is the model:

We can see the radiation dose in the X axis and the survival ratio in the Y axis.

D) Alpha is the linear component of the graph, while Beta is the quadratic or "curved" component. A linear behavior shows an early response and a curve behavior shows a late response. This is about the cells dying in the specific event of radiation or dying lately by the cumulative effect of the radiation. The curve in the graph shows a late responding cell line.