Analysis of Radiomodulatory Effect of Low-Level Laser Irradiation by Clonogenic Survival Assay

Objective: The aim of this study was to investigate the radiomoulatory effects of low-level laser irradiation (LLLI) in normal and cancer cells exposed to ionizing X-ray radiation on clonogenic survival assay. Background data: LLLI does have radioprotective effects on normal tissue. LLLI can reduce the incidence of mucocutaneous complications of ionizing radiation. Few in vitro studies reported adaptive responses for LLLI to ionizing radiation in normal and cancer cells, particularly with respect to clonogenic cell survival assay. Methods: Normal NIH 3T3 cells and cancer HeLa cells were irradiated with 685 and 830 nm LLLI at different energy densities prior to ionizing X-ray radiation. The survival fraction was determined after ionizing radiation (0, 2, 4, and 6 Gy). The values of the linear (α) and quadratic (β) parameters were calculated based on the clonogenic survival curves. Results: Clonogenic radiation survival assay showed that the application of LLLI at 685 nm prior to ionizing radiation could significantly inhibit clonogenic growth of HeLa cells compared with unirradiated HeLa cells. LLLI could also significantly increase the α parameter of the linear quadratic (LQ) model. In contrast, application of LLLI at 830 nm could significantly protect NIH 3T3 cells against radiation and decreased α parameter. Conclusions: This study suggests that various physical parameters of LLLI can be diverse adaptive responses to ionizing radiation on normal and cancer cells. Copyright © 2015, Mary Ann Liebert, Inc