Rat mammary carcinogenesis following neutron- or X-radiation

Episode von Medizin - Open Access LMU - Teil 02/22 von Ludwig-Maximilians-Universität München · 1. Januar 1974

Female 61 to 63 - day - old Sprague-Dawley rats were exposed once to a single dose of either 0.43 - MeV

neutrons or 250 - kVX - rays . For neutrons 23 rats were exposed in plastic tubes rotated around and 31 c m from

a water-cooled tritium impregnated target bombarded with 2.45 - MeV protons from a V a n de Graaff generator.

The mean kerma was measured at the rat location by integrating the response of a rat - sized homogeneous

tissue equivalent ionization chamber of minimum mass. The ratio between absorbed dose and kerma is under

investigation and is anticipated to be approximately 0.7. A compensated GM gamma-ray dosimeter indicated

that the gamma - ray doses were 3.5% of the total dose. All rats were examined weekly for the presence

of breast tumours and these were removed, fixed, stained and verified histologically as mammary neoplasms.

At 10 months after exposure 98<7ο of the rats were a live . The neutron kerma, the per cent of rats with

mammary neoplasia, and the number of rats were, respectively: 0.125 rads, 8.2°}o, 182; 0.5 rads, 9.0^0,

89; 2 rads, 20. 6,68; and 8 rads, 31.1%, 45. The X - ray results were: 30 R, 1.4% 95; 60 R, 27. l°Io, 48;

and 90 R, 35.4%, 48. A 3. O^o incidence was found in 167 control rats. At 10 months after exposure the

mammary neoplastic response after 8 rads of neutrons corresponds approximately to that after 60 - 90 R of

X - rays . Similarly, the response after 2 rads of neutrons was intermediate between 30 and 60 R of X - rays and

the response after 0 . 125 and 0.5 rads of neutrons was similar to that after 30 R of X - rays . This demonstrates

that the RBE for 0.43 - MeV neutrons is much lower at high doses than at low doses. Determination of the

confidence limits for the dose-RBE dependence and dose-incidence relationship will be determined as additional

data are collected.

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