Organ Differences in Response

6 Distribution of Radiogenic TUmors in Relation to Time After Exposure 

There is a characteristic temporal pattern in the occurrence of radiation-induced tumors following irra ation, a pattern that may be segmented into a latency period during which no excess is expressed, a period marked by a rise to a peak or a plateau that may be sustained, and a period of subsidence that may be absent. Only for leukemia and for bone cancer following uptake of radium-224 is this pattern well delineated a latency period of 2 to 4 years, a peaking at perhaps 6 to 8 years, and subsidence to near zero about 30 years after exposure. For other radiogenic cancers, the minimal latent period is less well defined and is generally taken to be 10 to 15 years. 

The degree to which the risks of radiogenic tumors other than leukemia peak rather than plateau is not well established. And whether, as assumed in the BEIR III Report (NAS/NRC, 1980), the expression of excess solid tumors extends throughout life also remains uncertain. The maximum foUow-up interval is about 40 years. But observations on the older A-bomb survivors, as well as on other series (Boice and Monson, 1977 Howe, 1984), give no grounds for believing that the 

Some imcertainty characterizes the relationship between dose and latent period for radiation-induced cancer in man, for the data are few and somewhat at odds with experimental findings. Animal experiments generally show a shortening of latent period with increasing dose (UNSCEAR, 1977 Ma3meord, 1978). Human data are seldom reported but the experience of the A-bomb survivors lends itself to the investigation of this issue, and a recent report (Land and Tbkunaga, 1984) provides substantial evidence that the latency of solid tumors may be independent of dose. 

7 Relation of Radiogenic Cancer Incidence to Natural Incidence 

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