Abstract
In order to measure in vitro radiosensitivity, clonogenic assay has been the gold standard for evaluating overall consequences of early and late responses to radiation. Since clonogenic assay relies on the ability of cells to form viable colonies derived from "a single cell", it is not directly applicable to cells with very low plating efficiencies. Moreover, this assay ignores the cell-to-cell communication because cells are usually plated out at very low density to form colonies from single cells. To overcome these problems, the "high density survival" (HDS) assay was recently developed. In this study, we developed the modified HDS assay which is easier to be performed. We have recently defined and established radioresistant cells with clinical relevance. Those radioresistant cells continued to proliferate with daily exposure to 2 Gy of X-rays for more than 30 days. The modified HDS assay successfully detected clinically relevant radioresistance which is not always observed by colony assay or other ordinary assays for cell survival and death. Therefore, we think that the modified HDS assay in the present assay is a useful tool to predict radioresistance with clinical relevance.
