The Late Effects Of Terminated Protracted Whole-Body 60 Co Gamma Irradiation On Beagle Dogs

Abstract

Beagle dogs exposed to protracted Co gamma irradiation were observed for late effects, particularly life shortening ® and fatal tumor incidence. A total of 86 controls and 136 irradiated beagles entered the study, with 60% of these dead as of October 1, 1983. A nearly equal number of beagles of both sexes began If-ray exposure at 400 days of age. The 6 0 Co ¥-rays were given to predetermined total exposures of 600, 1400, 2000, and 4000 R at rates of 5, 10, 17, and 35 R/ day (22 hours/day, 7 days/week), with a few exceptions. Although 40% of the beagles are still alive, interim data for the median (50%) times to death for the various groups suggest that both dose rate and total dose affect survival times. Compared to the median survival of the control population [4341 ± 139 (SEM) days], all irradiated groups showed appreciable life shortening. The mean time to death for the irradiated dogs [2604 ± 89 (SEM) days], irrespective of the dose rate or total dose, is considerably shorter than that for the control group [3504 ± 199 (SEM) days]. In contrast to dogs given continuous whole-body irradiation, those given protracted irradiation to predetermined total doses died largely of causes unrelated to the hematopoietic system. The dogs receiving terminated exposures exhibited an obvious recovery from hematopoietic damage after irradiation was terminated, then died at later times of soft tissue malignancies. Although there have been far fewer myeloproliferative disorders (MPD) in the terminated exposure groups than in continuously irradiated dogs, they are a significant number compared to the controls as no cases have been seen in the control dogs. Death rate analysis of fatal tumors indicates a significant positive trend of tumor deaths in the irradiated dogs and a significant shortening in the time of death for individual tumor types as compared to controls. The mammary gland was the origin of more malignancies than any other site, with the mean time of death due to the tumor significantly shorter for the irradiated dogs [3011 ± 125 (SEM) days] than for the controls [3981 + 237 (SEM) days]. The incidence of sarcomas and carcinomas was also significantly greater in the irradiated dogs as compared to controls. Reports from this study agree quite well with those obtained from rodents and illustrate important differences as compared to continuous irradiation.