Purpose: There is growing interest in developing individually tailored cancer radiation therapy (RT), wherein patients with high intrinsic radiosensitivity are identified before commencing treatment, to minimize severe adverse reactions. In a previous retrospective study of severely radiosensitive RT patients, we established a functional assay with a high predictive capability. The assay involves ex vivo irradiation of peripheral blood mononuclear cells and analysis of DNA repair using the γ-H2AX assay. It is unknown whether RS is a fixed phenomenon or is modulated under different conditions. We now report the impact of RT on the apparent radiosensitivity, as reflected by the assay.
Methods and materials: Peripheral blood mononuclear cells of 11 patients with non-small cell lung cancer were collected before, during, and after RT. Quantitative parameters derived from the nonlinear regression analysis of γ-H2AX foci were applied to examine the cellular radiation response.
Results: Although the repair rate and foci yield remained constant during and after RT, the "unrepairable" component of γ-H2AX foci decreased over the course of treatment in 7 patients, signifying a generally enhanced DNA repair capacity. Interestingly, enhanced repair capacity tended to be associated with a poorer response to RT.
Conclusions: Although generalization of these results into normal and tumor tissues warrants further investigation, the findings of this study have important implications in future strategies for identifying radiosensitive individuals before exposure to RT. We can anticipate that the threshold values that will discriminate radiosensitive patients in a future prospective trial will differ from those established in the retrospective study.
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