title: The r.b.e. of fast fission neutrons (2 MeV) for chronic radiation damage of the large bowel of rats after single dose and fractionated irradiation.
abstract: Late damage in the rectum of rats was studied after local irradiation with 2 MeV fast fission neutrons and the results were compared with those for 300 kV X-rays. A similarity between latency times, and between clinical, gross pathological and histological appearances of the rectal obstruction after the two types of radiation was observed. The r.b.e. evaluated from ED 50/200 days values was 1.8 for single doses, 2.1 for two fractions and 3 for five fractions and these are similar to r.b.e.s from other investigations of chronic intestinal radiation damage. Using linear quadratic analysis, a limiting r.b.e. of 5 was obtained. The beta-values are similar for both radiation qualities. Because of the high gamma-contamination (25 per cent) in the RENT I beam a possible correction of the r.b.e. for neutrons only, assuming interaction, is discussed.
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005214:Fast Neutrons; D005260:Female; D009502:Neutrons; D011833:Radiation Injuries, Experimental / Q000473:pathology*; D051381:Rats; D012007:Rectum / Q000473:pathology / Q000528:radiation effects*; D012062:Relative Biological Effectiveness; D013997:Time Factors