Status of the Dosimetry for the Radiation Effects Research Foundation (DS86) (2001) / Chapter Skim
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7. Implications for Risk Assessment
7. Implications for Risk Assessment
Pages 87-94
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From page 87... ...
In line with the principal aim of the studies at RERF the elucidation of the health effects among the survivors it is reliably known from 5 decades of epidemiological follow-up what the specific radiation exposures in Hiroshima and Nagasaki have done and what past and continuing risk they have posed for the survivors (Thompson and others 1994; Pierce and others 1996~. The increased cancer rates have been thoroughly studied in their dependence on distance from the hypocenter and on shielding.
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From page 88... ...
Therefore, although this report' s evaluation of the discrepancies between measurements and DS86 calculations should not, and does not, depend on how the resolution of the discrepancies might affect estimates of radiogenic risk, it is appropriate to consider in a preliminary way whether modifying the dosimetry system to reduce the discrepancies will greatly affect risk estimates. To be relevant to risk estimation, discrepancies between calculations and measurements of neutron fluence in DS86 must occur in a dose range where health effects due to the radiation exposure have been ascertained, and the neutron doses in this range must be large enough to contribute substantially to the observed effects.
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From page 89... ...
Solid curves correspond to the current dosimetry system, DS86; dotted curves to neutron doses increased in line with thermal-neutron activation data (Straume and others 1992~; broken curves to intermediate adjustment that might be consistent with preliminary 63Ni measurements (Chapter 3~.
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From page 90... ...
Although the relatively high dose of 1 Gy might seem to be in line with fairly low values of the neutron RBE, it must be recognized that in DS86, at a 1 Gy total dose to the bone marrow in Hiroshima, the neutron dose is only about 15 mGy. That is in the lower range of neutron doses at which excess tumor incidence has
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From page 91... ...
Because of the linear dose dependence for neutrons, the 15 mGy of neutrons will contribute 0.3 En to the observed effect Fobs = (0.985+0.3) En = 1.285 En at 1 Gy total absorbed dose.
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From page 92... ...
COMPARISON OF NEUTRON EFFECTS IN HIROSHIMA AND NAGASAKI If the same calculations are made for Nagasaki with only one-third as great a neutron contribution as that in Hiroshima 5 mGy instead of 15 mGy at a 1 Gy total absorbed dose then the calculations can be summarized as in the following table (Table 7-1~. The results in Table 7-1 show that from a consideration of reasonable RBEs for neutrons, the effects to be expected for the same total absorbed dose of 1 Gy should be 18 40% higher in Hiroshima than in Nagasaki only because of the greater number of neutrons in Hiroshima, as calculated in DS86.
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From page 93... ...
With the full modification of Straume and others 1992 (see dotted line in Figure 7-1) the neutron/gamma ray dose ratio at a 1 Gy total dose would be 0.055.
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From page 94... ...
There is some conflict between the general experience, in radiobiological studies, of upward curvature in the dose-effect relations and the finding that the dose dependence for solid tumors in Hiroshima and Nagasaki is seemingly linear. More curvature is, of course, indicative of a lower risk coefficient for gamma rays.
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