Abstract
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Objectives A comparison of dose-rate-dependent effects of internal and external radiation onviability and DNA strand breaks in thyroid carcinoma cells.
Methods Cells of a well-differentiated thyroid carcinoma (B-CPAP) were exposed to internal (I-131: 1-147Gy, 5x10-4-0.448Gy/min) or external radiation (linear accelerator: 0.5-60Gy, 4Gy/min). Decrease in cell viability (measured by cleavage of tetrazolium salt WST-1) and the extent of DNA damage (using Fluorometric Analysis of DNA Unwinding) were evaluated. DNA damage was assessed immediately after radiation and cell viability was measured 5-6 days after start of irradiation.
Results External and internal radiotherapy caused a significant (p<0.0001), dose-dependent increase of DNA strand breaks. In parallel cellular viability decreased (p<0.0001). External radiation caused a higher amount of DNA strand breaks and affected viability more severe than internal radiotherapy. This effect was dose-dependent and increased with rising doses (Fig. 1). At a dose of 30Gy viability was 2-fold higher after internal radiotherapy (78 vs. 41%) and DNA strand breaks were 15-fold lower (85 vs 5% DNA remaining double-stranded).
Conclusions In our experiments external radiation led to a stronger cytotoxic effect regarding DNA damage and cell viability. At identical overall doses, external radiation, due to its higher dose-rate, caused a greater radiation damage suggesting that internal radiation allowed DNA repair during radiation.
- © 2009 by Society of Nuclear Medicine