Masato Ito, Presenter: Nothing to Disclose

Chikao Sugie, Abstract Co-Author: Nothing to Disclose

Hiroyuki Ogino MD, Abstract Co-Author: Nothing to Disclose

Yuta Shibamoto MD, Abstract Co-Author: Nothing to Disclose

Previous studies have demonstrated significant radioprotective effects of low-dose priming irradiation with 300-500 mGy against subsequent lethal dose irradiation in ICR mice. The purpose of this study was to investigate whether or not such a radioprotective effect was observed in the same mouse strain at lower doses (30-60 mGy) that are used in diagnostic radiology.

Six-week-old male ICR mice were used. The mice received whole-body irradiation with 10 or 20 mGy at a dose rate of 40 mGy/min for 3 days at 24-h intervals. Control groups were sham-irradiated. On the fourth day, the mice were exposed to mid-lethal or lethal doses (5.5-8.0 Gy) at a dose rate of 1 Gy/min. 32 mice were used for each group and were observed for 30 days. The difference in survival curves were examined by the logrank test. In the experiment using a dose of 5.5 Gy, priming irradiation with 50, 100, and 200 mGy was also given for 3 days to the other three groups of mice.

The 50% lethal dose appeared to be around 5.75 Gy in the ICR mice. In the experiment where 6 Gy was given on day 4, the 30-day survival rate was 22% in the control sham-irradiated group, 34% in the group preirradiated with 10 mGy for 3 times, and 28% in the group preirradiated 3 times with 20 mGy, but the difference was not significant. In the experiment using 5.5 Gy, the 30-day survival was 69% in the control group, 78% in both the 10-mGy- and 20-mGy-preirradiated groups, 78% in the 50-mGy group, 75% in the 100-mGy group, and 56% in the 200-mGy group. The survival rate of the group preirradiated with 200 mGy for 3 days tended to be lower than the rates of the 10-, 20-, and 50-mGy-preirradiated groups (p < 0.1), but there was no significant difference between the control group and pre-irradiated groups. In the experiments using higher doses (6.5-8 Gy), there were no differences in survival curves among the control, 10-mGy-pretreatment, and 20-mGy-pretreatment groups.

With the priming doses of 10 or 20 mGy given for 3 days, no radioprotective effects of preirradiation against subsequent mid-lethal or lethal dose irradiation were observed. However, there was no deteriorating effect of these low doses of radiation.

Ito, M, Sugie, C, Ogino, H, Shibamoto, Y, Effect of Low-dose Whole-body Radiation before Mid-lethal or Lethal Radiation on Survival of Mice.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4413738.html