Cellular effects of high-intensity focused continuous wave ultrasound alone and in combination with X-rays.
OBJECTIVE
To investigate the cellular effects of 1.1 MHz high-intensity focused continuous wave (CW) ultrasound alone and in combination with X-rays.


METHODS
V79 cells were exposed to ultrasound of different intensities for 30s (non-hyperthermic conditions). In the combined treatments, cells were exposed to ultrasound (63 W/cm2) either before or after 2 Gy X-irradiation. Cellular effects studied were clonogenic survival, DNA strand breaks (pulsed-field gel electrophoresis, DNA precipitation assay) and membrane integrity (morphological analysis).


RESULTS
With increasing ultrasound intensity, cell survival decreased in a dose-dependent manner as the induction of DNA strand breaks, the fraction of cells with lost membrane integrity and cell lysis increased. In the treatments with combined exposures, the regimen with X-rays before ultrasound had a nearly additive effect on cell kill, whereas the reverse regimen with ultrasound exposure before X-irradiation resulted in a synergistic effect (p<0.012).


CONCLUSIONS
High-intensity focused CW ultrasound induces an intensity-dependent reduction in clonogenic survival in V79 cells, which seems to depend on both DNA and membrane damage. Combined exposures of ultrasound and X-rays resulted in a synergistic reduction in cell survival when cells were exposed to ultrasound before X-rays but not for the reverse regimen. Thus, a larger fraction of the repairable sublethal cell damage induced by an initial ultrasound exposure was rendered non-repairable by a subsequent X-ray exposure than if the reverse treatment order was used.
Jernberg
A
A
Division of Medical Radiation Physics, Karolinska Institutet, Stockholm, Sweden. annica.jernberg@cck.ki.se
Edgren
M R
MR
Lewensohn
R
R
Wiksell
H
H
Brahme
A
A
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D006224:Cricetinae; D004247:DNA / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D015233:Models, Statistical; D013997:Time Factors; D014465:Ultrasonics / Q000009:adverse effects*; D014965:X-Rays / Q000009:adverse effects*
D004247:DNA