ringworm with radiation, the report noted that tumors began to appear about 20 years after exposure and were not limited to the most heavily irradiated parts of the scalp. Tumors tended to occur more commonly at the margins of the scalp and in neighboring areas of skin that were not covered by hair or clothing. An excess of skin cancers was detected even on the cheeks and the neck, where the doses were estimated to have been only 0.12 and 0.09 Gy (12 and 9 rad), respectively. The distribution of tumors suggested that the carcinogenic effects of X rays were increased by exposure to UV radiation.

In 1991, the ICRP stated in Publication 59 (ICRP, 1991b) that “although it has traditionally been thought that there was little if any risk of skin cancer below 10 Gy [1,000 rad], there are now several sets of data indicating excess skin cancer following doses of a few grays [a few hundred rad], with one study suggesting risk below 1 Gy [100 rad]. The evidence does not indicate that the risk per unit dose is greater at higher doses than at lower [doses].” The ICRP also noted that risks were greater for UV-irradiated skin.

Thus, by 1991, there was ample indication from authoritative national and international bodies that skin cancer could be caused by doses much lower than 1,000 rad and that UV-exposed skin was particularly sensitive. However, it was not until 1998 that this information began to be incorporated in dose reconstructions for atomic veterans who filed claims for skin cancer.

V.C EVALUATION OF METHODS OF ESTIMATING INTERNAL DOSE

V.C.1 Introduction

Doses due to intakes of radionuclides produced in a nuclear detonation often are considered to be unimportant when compared with doses due to external exposure. That is especially the case in exposure scenarios involving inhalation of fallout particles at locations relatively close to ground zero and shortly after detonation (NRC, 1985b; Levanon and Pernick, 1988; IOM/NRC, 1995). Such an exposure scenario is important for many participants in nuclear tests at the NTS and in the Pacific. The unimportance of the inhalation hazard posed by fallout shortly after a detonation, compared with the hazard posed by external exposure, is attributed to such factors as: the presence of much greater activities of short-lived photon-emitting radionuclides that tend to result in high external doses per unit activity but much lower inhalation doses, compared with the activities of longer-lived radionuclides for which inhalation doses per unit activity often are considerably higher; the dominance of large, essentially nonrespirable particles in fallout relatively close to ground zero; and the insolubility of fallout particles, which can substantially reduce the extent of absorption of inhaled radionuclides into the body. However, there are exposure scenarios for participants at the NTS and in the Pacific in which activities of longer-lived radionuclides compared with



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