English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

THE INACTIVATION of cells by ionizing radiation is usually described by determining the proportion of the population which survives a given radiation exposure. Cells grown in vitro are irradiated, counted and plated into Petri dishes, and then incubated at 37°C under growth conditions. After incubation for a prescribed time, the fraction of cells capable of forming a colony of 50 or more cells is determined; these cells are defined as survivors and the logarithm of the fraction of surviving cells, log S, is plotted as a function of dose (Puck & Marcus, 1956). Measurements in the low-dose region are limited because one is faced with measuring the surviving fraction in a population of predominantly surviving cells. Even when the survival experiment is performed with the utmost care, it is not possible to determine S with precision greater than 10%. In a log S vs D plot, the absolute errors in log S are of the same magnitude throughout the dose range. Thus at low doses (S between 1-0 and 0.5), such uncertainties do not permit determina-tions of radiobiological parameters (e.g. the oxygen enhancement ratio (OER), relative biological effectiveness (RBE) of different radiation modalities, cell-cycle dependence, effects of radiosensitizers and protectors) with sufficient precision to ascertain whether or not these parameters change at low dose as compared to higher doses. The uncertainties in such survival measurements arise primarily from uncertainties in the number of cells plated on the first day. Errors in the counting of cells in suspension, multiple dilutions before plating and the plating itself are all contributory factors. We have developed a method whereby survival of cells is measured with significantly < 10% error. This method is particularly applicable at surviving fractions between 1-0 and 0-5 which corresponds to dose levels between 0 and 3 Gy. We followed the fate of single cells, plated and identified on Day 1, through the incubation period of 7 days using an inverted microscope. By determining the number of cells which on the 7th day produced a colony of > 50 cells, we were able to establish the exact number of surviving cells (S) as well as the number of killed cells (K). The method of looking at individual cells has been proposed before (Bedford & Griggs, 1975); however, the importance of measuring K (as well as S) was not recognized. We have used this technique to study the effect of oxygen at …

Survival measurements at low doses: oxygen enhancement ratio