+ 2713/2881 12:25 37843. RAD HEALTH SCIS PAGE 81/82

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Port Collins, Golorado 80523-1673
(970) 491-5222

FAX: (970) 493-0623
hitp/Avww.colostate.edu/Depts/RHS

Voice: (970) 491-6674
FAX: (970) 491-7742
December 11, 2001]

James W. Neton, Ph.D., CHP

National Institute for Occupational Safety and Health, MS-R45
Office of Compensation Analysis & Support (OCAS)

4676 Columbia Pkwy

Cincinnati, OH 45226-1998

Dear Dr. Neton:

T have carefully reviewed the draft document entitled “Proposed radiation weighting factors for
use in calculating probability of causation of cancer”. In doing so I have spent approximately 3
days reading the manuscript, examining calculations, and reviewing relevant literature on which
their conclusions are based. In particular, I have focused on calculations for neutron RBE
values. In general the report is very well done and quite clear. ] would however suggest, that the
concept of differences in radiation interactions in smal} mammals versus humans (recoil protons
versus gamma rays) and its impact on biological effectiveness, which is carefully stated in, the
first full paragraph on page 5 be move forward in the manuscript as a general concept on page 1
paragraph 2. Also on page J paragraph 2 line 5 it is stated that values of radiation weighting
factors are selected to represent data on RBE-I would rephrase to state “take into account
data...” and then discuss in general terms interactions of high let in small versus large animals.

Another concern is the distribution of RBE values for neutrons in the experimental data. The
authors state on page 5 linesS and 6 that more than 60% of the RBE values are below the
arithmetic mean of 6. They state that this can be justified by different interactions between small
and large animals-however a careful look at the life-shortening and tumor data suggest an
alternative explanation that need to be taken into consideration. The low RBE values for life-
shortening are mainly related to studies in RF and RFM mice for which the principle cause of
death and the greatest contributor to life-shortening are leukemias and lymphomas (myeloid
leukemia and thymic lymphoma specifically). AJ] of the tumor induction data suggest low
RBE’s for leukemias and lymphomas but higher RBE values for solid cancers-this is born out
not only by the incidence data for individual tumors but also by the life-shortening data in the
B6CF! data where the causes of death are more often a result of solid tumors rather than
leukemia. In all these instances neutron RBE values tend to be higher. The skewing of the RBE
values to the lower end is most likely a result of a preponderance of data using RFM mice and
their tendency to develop early appearing leukemias and lymphomas rather than solid cancers.

University Program of Research and Scholarly Excellence in
“Radiological Health Sciences and Cancer Research”



“12/1/2901 12:25 3784917742 RAD HEALTH SCIS

Perhaps differences in RBE values for leukemia/lymphoma versus solid cancers should be
considered in this report.

Sing)

rich

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