Abstract # 2676 Biological Effect of Intermittent Radiation Exposure: Recovery from Sublethal Damage Versus Reoxygenation in Vivo

Presenter: Tomita, Natsuo

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Results:
In the first experiment using clamped tumors, cell survival tended to increase with elongation of the interfraction interval, although the increase was not so clear as seen in our in vitro study. In the second experiment, no reoxygenation was seen when the interval was 0 or 2.5 min (hypoxic fraction: 100%), but when the interruption was 5 min, the hypoxic fraction decreased to 53% (95% confidence interval: 34%-83%), indicating a significant reoxygenation within 5 min. In the growth delay experiment, the effect of 25 Gy given in 5 fractions at 3-, 6- or 10-min interfraction intervals was significantly lower than that of 25 Gy given continuouslty. The effect tended to decrease with elongation of the interfraction intervals (growth delay time: 3-min interval group > 6- or 10-min interval groups).




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