[Intestinal tolerance in mice after low dose rate 60CO irradiation. Implications for radiotherapy]

Influence of absorbed dose rate has been studied in BALB/c mice for early intestinal tolerance. After selective abdominal irradiation, LD50 at 5.5 days increases from 12.36 to 20.22 and 21.79 Gy when dose rate decreases from 0.61 to 0.054 and 0.026 Gy/mn. LD50 at 6.5 days increases from 12.05 to 19.22 and 21.58 Gy respectively. The LD50 ratios are then 1.6 and 1.8 for both endpoints. After total body irradiation. LD50 at 5.5 days increases from 9.92 to 15.20and 16.83 Gy when dose rate decreases from 0.56 to 0.049 and 0.024 Gy/mn. The corresponding LD50 ratios, i.e. 1.5 and 1.7, are then similar to the former ones. Increase of LD50 when decreasing dose rate is in agreement with that expected taking into account only repair of sublethal lesions, for the generally accepted cellular models.