The short-time restraint of pregnant mice on day 8 of gestation led to a significant increase of the anomaly rate in fetuses. This effect may be due to stress factors of endocrine origin.

Mature oocytes (class A) and immature oocytes (class B) from a repair-proficient yw strain and two repair-deficient strains (mus 302D1 and mei 41D5) were initially X-irradiated with 0.02 Gy and subsequently treated at various time intervals with 2 Gy. They were tested for dominant lethality (early and late death). For each strain and stage the observed values were below those expected on the basis of additivity of the effects of the two irradiations given separately. These results indicate the existence of a repair-stimulating effect of low doses for the repair-deficient strains as well as for the highly radiosensitive mature oocytes. This 'adaptive response' was highest for mei 41, lower for yw and lowest for mus 302, and also involved 'late death' lethality (real dominant mutations). The finding that the two repair-deficient strains showed significant differences in normal dominant lethality, as well as in radiosensitivity and adaptive response, is consistent with dissimilarities in the repair defect.

Pregnant mice of two different strains (F/A and NMRI) were exposed to 1 rad of whole-body pion- or X-irradiation at day 8 of gestation. Lucanthone (Miracil D), a known radiosensitizer in various biological systems, was applicated 30 min before irradiation. Five days after treatment the fetuses were observed for developmental anomalies. In both strains of mice it was found that the radiation dose as low as 1 rad results in a significant increase in the rate of abnormal fetuses compared to nonirradiated, but restrained fetuses. Comparing the effectiveness of negative pions (peak irradiation) with X-rays for teratogenic effects, the RBE was between 1.7 and 1.9. The application of Lucanthone increased the number of damaged fetuses and led to various degrees of sensitization depending on the mouse strain and dosage used. Differences between the strains as regards the frequency of damages are explained by different development stages at the time of treatment.

No abstract

Greene melanoma in the anterior chamber of rabbits was irradiated by protons to find the isoeffect curve for proton irradiation fractionated into one, two, three or four doses. The isoeffect curve for tumor tissue remained constant between one- and three-dose fractionations and rose with four-dose fractionation. The isoeffect curve for normal tissue approximately followed the Ellis equation. Therefore, the optimal irradiation schedule should be in the range of three fractions because this best spares normal tissue while delivering a tumoricidal dose to the lesion. The relative reduction of the total dose from four- to one-dose fractions of intraoperative irradiation should be 20%.