Effect of radiation dose rates and cisplatin on cytogenetic damage in rats receiving head-neck radiotherapy.

Background: We aimed to investigate effect of radiotherapy (RT) applications with different dose rates on cytogenetic damages, which focused on micronucleus (MN) formation, and evaluate how this damage varies by cisplatin in rats receiving head-neck RT.
Material and Methods: Thirty-six Sprague Dawley rats were divided into five groups. The first and second groups were irradiated at a dose rate of 300 monitor unit/minute (MU/min) and 600 MU/min, respectively. The third group was irradiated at a dose rate of 300 MU/min and given cisplatin. The fourth group was irradiated at a dose rate of 600 MU/min and given cisplatin. The fifth group received neither irradiation nor cisplatin (control group). One thousand polychromatic erythrocytes were scored, and MN frequency in polychromatic erythrocytes was determined for each rat.
Results: There was a significant difference among five groups in terms of the number of MN (p: 0.001). The number of MN was significantly higher in the 600 MU/min + cisplatin group (fourth group) compared to the control group [9.5 (1.0-23.0) vs. 1.5 (1.0-2.0), respectively]. It was also significantly higher in 600 MU/min + cisplatin group (fourth group) compared to 300 MU/min group (first group) [9.5 (1.0-23.0) vs. 2.0 (1.0-3.0), respectively]. On the other hand, there was no significant difference among other groups.
Conclusions: Our findings suggest that RT given at a higher dose rate causes more cytogenetic damage, and this damage is increased by concurrent administration of cisplatin.
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