SO WL Robison SS BW Wachholz mi vei OV Date July 9, 1979 To North Marshall Islands Advisory Group from R. 0. Gilbert subject’ An Approach for Assessing the Validity of the 3xRule for Estimating the Maximum Individual Dose. Should the Method be Used for the Enewetak Dose Assessment? 0.0. Cetbeat NS No 409836 nae in FOLOER BOX No. COLLECTION Marshal! estimate of the “maximum individual" dose, where x is the estimated maximum annual dose as computed using average values for the diet and food j pate “29/7 2 concentrations. LLL argues that 3x may be equal to the 95th percentile or so of the dose distribution over individuals, so that the probability of an individual receiving an annual dose greater than 3x is very small. The validity of this approach is open to question, of course, since we don't know what the actual distribution of doses will be for any given year following the return of the Enewetak people to the Enewetak Atoll], if that return KECTE should take place. Reviewed by REPOSITORY Internal Oistibaten Pacific Northwest Laboratories I have been thinking about LLL's proposed procedure of using 3x aS an DOCUMENT DUES NU'T CONTAIN ECI ¥N Nt Ls lands SPs Entwtlak June-July “79 %« Ballelle Personally, I would feel more confident about the 3x approach if LLL could demonstrate via computer simulations that this factor of 3 is reasonable. These simulations could be based on the diet information from Michael Pritchard's recent survey of the Enewetak people, and upon the soil and plant/soil ratio data now available. The basic idea would be to generate the projected dose by specifying distributions for each of the input parameters of the model, e.g., Bennett's model for Sr-90 in bone. The model itself would be assumed to be correct, If the resulting variability of the generated dose distribution was such that, say, 20 or 30 percent of the distribution was greater than 3x, then we might consider using 4x or some other factor that did reach out into the 99 percentile or so. On the other hand, if the value 3x was greater than 99 percent of the distribution under worst case conditions, I would feel more comfortable with the factor 3. Of course, the simulation results would prove nothing since we don't have a very good handle on the distributions of the various parameters involved. But, by going through the simulation process and generating the dose