Claire J. Shellabarger

Assessment of Risk from Low-Level Exposure to Radiation and Chemicals

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Radiation carcinogenesis: laboratory studies.

A brief review of animal studies following external radiation suggested the following generalizations. For low LET radiation several different dose‐response relationships were obtained over a wide range of doses; lengthening the time over which the radiation is given generally lowers the risk of tumor induction. For high LET radiation the dose‐response relationship usually appears to be linear and lengthening the time over which the radiation is spread does not lower the risk of tumor induction. No single RBE value for high LET radiation for tumor induction can be given but current studies point in the direction of an inverse relationship between RBE value and dose. Animal studies of radiation carcinogenesis provide information of more qualitative than quantitative significance in regard to human radiation carcinogenesis.

Dedication: To Our Colleague and Friend Dr. Charles Little Dunham

This volume is dedicated to the memory of Dr. Charles Little Dunham, Director of the Division of Biology and Medicine, U. S. Atomic Energy Commission from 1955 until 1967 and Chairman of the Division of Medical Sciences, National Academy of Sciences from 1967 to 1974.

Mammary Neoplasia in the Female Rat After Neonatal and/or Adult 7,12-Dimethylbenz(a) Anthracene Administration

Summary At 175 days of age it was found that DMBA given to female Sprague-Dawley rats at 2 days of age was followed by a high incidence of mammary fibroadenoma. DMBA given at 52 days of age was followed by a high incidence of mammary adenocarcinoma. When both DMBA treatments were given to the same animals, the mammary adenofibroma incidence was much the same as in the rats given only DMBA at 2 days of age and mammary adenocarcinoma incidence was much the same as in animals given only DMBA at 52 days of age. No significant interaction between two doses of DMBA given at both 2 and 52 days of age on mammary neoplasia was noted.