Nonmonotonic behavior of the dose dependence of the radiation effect on cells in vitro exposed to pulsed laser radiation at lambda = 820 nm.

BACKGROUND AND
OBJECTIVE: In recent years, clinical low-intensity laser therapy practice has used pulsed radiation, mainly from semiconductor lasers. Experimental works devoted to the study of relationships between biological and clinical effects and parameters of pulsed radiation are practically absent. STUDY DESIGN/
MATERIALS AND METHODS: The radiation source was a laser diode emitting at 820 nm (292 and 700 Hz, duty factor 80%; doses from 7 J/m2 to 5 x 10(5) J/m2; intensities 4, 12, 51, 152, 633, and 1,900 W/m2; irradiation time from 1 to 30 s). Four biological models were used: nucleated cells of murine spleen (splenocytes) and bone marrow (karyocytes), murine blood, and HeLa cells cultivated in vitro. The intensity of luminol-amplified chemiluminescence (in case of murine models) and the adhesion of HeLa cell membranes were measured as a function of the irradiation dose.
RESULTS: Within the wide exposure dose range used we obtained seven maxima in the dose vs. biological effect curves: at fluences near 20, 1 x 10(2), 3 x 10(2), 8 x 10(2), 3 x 10(3), 1 x 10(4), and 3 x 10(4) J/m2. The peaks coincided for all four models.
CONCLUSION: The dose curves obtained with different cellular systems are of the same type and are characterized by seven peaks in the dose interval studied (7 J/m2 to 5 x 10(5) J/m2).