|Tumours and Lifespan in Rats After Gamma Irradiation At Different Ages
|Published: Open access to everyone
|Dr. Michele Morin
|BIOLOGICAL SAMPLE AVAILABLE
|Purpose: To determine the effects of age and the dose rate reduction factor for external gamma irradiation.
Status: 1982-1990, terminated, data in ERAD
Treatment: Exposure to a low dose rate Co-60 gamma source at different ages and dose rates
Dosimetry: Ionization chamber
Endpoints: Life-span study (spontaneous death) with macroscopic/microscopic pathology
Animal: Sprague-Dawley SPF rats of both sexes
Results: Epidemiological studies so far did not reveal an increase in cancer incidence among people occupationally exposed to small doses of radiation at low dose rates with exception of alpha ray exposure; risk assessment thus depends on an extrapolation form data on high doses/ dose rates. Studies on experimental animals should therefore clarify whether a reduction in dose rate is accompanied by a reduction in radiation-induced cancer. The doses used varied between 1 and 39 Gy and were delivered at dose rates from 1.34 mGy/ h to 15 Gy/h.
A comparison between two groups of rats receiving 3 Gy Co-60 gamma exposure either at 1.34 Gy/h during 14 weeks or 78 mGy/h during 5 days demonstrated a reduction in the incidence of carcinomas by a factor of 5 at the low dose rate.
Since these exposures were still relatively short compared to the lifespan of the animals, it seemed important, for an assessment of the risk of long term exposure, to study the influence of age on the carcinogenic effect of radiation. Exposure to 3 Gy at an age of 9 months, 3 months or in utero showed little difference in cancer incidence compared to controls for rats aged 9 months whereas a significant increase was seen for rats exposed in utero or at an age of 3 months. The excess cancer incidence was only a 1/10 for the rats irradiated at 9 months compared to those irradiated in utero. The excess cancers after in utero exposure were mainly due to the great sensitivity of the central nervous system and the sex organs during their organogenesis.
|Link to data and details in ERA
|LINK TO FILE