The Standard-Setting Process

[hwade@triax.com (H. Wade Patterson)]

Group:
Those of you who have read my paper in the March issue of Health Physics
may remember that I claimed that standard-setting groups had overlooked,
and left unconsidered, data that was pertinent to the response of humans
to low doses of radiation. In my paper, I gave some examples. Here's
another.

The citation is: Mayneord, W. V.; Clarke, R. H. Carcinogenesis and
Radiation Risk: A Biomathematical Reconnaissance. Brit. J. Radiology
Supplement 12 :88; 1975
(In 1975, when this paper was written, William Mayneord was a consultant
to the British National Radiation Protection Board (NRPB), and Roger
Clarke was employed at Berkeley Nuclear Laboratory).

Here are some selected quotations from the text, followed by personal
comments.

Quotations from Section 1.3-The significance of the number of cells at
risk:

Quotation:
"The basic concept lying at the root of much theoretical work on
carcinogenesis is that a chance transformation or possibly a series of
such transformations, leads to an overt malignant tumor.( references
omitted) A second often hidden assumption, is that the transformation
and emergence of a single cell will lead to malignant disease and the
death of the whole organism. If we accept these theses, since the chance
of emergence of a single transformed cell from a uniformly irradiated
mass of similar cells is proportional to the number of cells at risk it
follows that the chance of death for a given dose would, for "similar"
organisms, be proportional to the mass of the organism."

(paragraph omitted)

Quotation:
"One of us has for some years proposed to himself (and to politely
amused friends) the apparently facetious but fascinating question 'Why
don't elephants all die of cancer?'"
( sentence omitted)
"Similar questions have been asked by Brues (1958, 1959) and have
recently been taken up again in an excellent paper by Dawe (1969) asking
why do not large animals develop neoplasms with a much higher incidence
than small ones since the cell population at risk is greater by many
orders of magnitude."

(paragraphs omitted)

Quotation:
"The reader may add this to his collection of teasing numerical
oddities. We will not pursue this very speculative topic further in this
text but briefly state that when we consider a very wide range of
species and conditions we have been able to find in the literature very
little evidence for any corresponding correlation of tumor incidence
with size, i.e., number of cells at risk. This conclusion is borne out
in a recent survey by Priester and Mantel (1971). Only in dogs is there
any limited correlation with size, and even here the rule is by no means
universal".

(These are the references to the above citations)
Brues, A.M. 1958, Critique of the linear theory of carcinogenesis,
Science, 693-699
Brues A.M. 1959, Somatic effects of low level irradiation, Amer. Assoc.
for the Advancement of Science, Publication 59, p.73
Dawe, C.T., 1969, Neoplasms and related disorders of invertebrate and
lower vertebrate animals. Philogeny and Oncogeny, National Cancer
Institute Monograph 31 (US Dept. of Health, Education and Welfare)
Priester, W.A., and Mantel, N., 1971, Occurrence of tumours in domestic
animals, Journal of the National Cancer Institute, 47, 1333.


Quotation:
"It is obvious that the mere total mass of cells in a large organism is
likely to prove a very poor indication of its susceptibility to cancer."

Quotation from Section 13-Conclusions:
"The 'multiple event' basis for example has made little impact on
radiation studies and this has led to an almost axiomatic assumption of
linear relationships not at all generally acceptable in the wider
field."


Comments:
What the authors have done is to treat a variety of radiation exposure
scenarios in the most mathematically rigorous manner possible, given all
the uncertainties of radiobiology. The impression with which this reader
is left, is that, while the linear no-threshold response is a
theoretical possibility, it is most unlikely.

Lest one think that my opinion is formed by taking the quotations out of
context, this paper was also reviewed in the UNSCEAR 1986 Report,
"Genetic and somatic  effects of ionizing radiation", United Nations,
New York, 1986.

Here is a quotation from that report. "the theoretical analysis by
Mayneord and Clarke (1975) does not support an overall linear
[non-threshold] relationship between dose and cumulative tumor rate over
finite time intervals in populations having a standard age
distribution." 
(Participants in the preparation of the UNSCEAR report included, B.
Lindell, J. Dunster, F.D. Sowby, W.K. Sinclair, and H.O. Wykoff).

This quotation from UNSCEAR 1986 also appears in ACRP-18, Biological
Effects of Low Doses of Radiation at Low Dose Rate, Advisory Committee
on Radiological Protection, Atomic Energy Control Board of Canada,
Ottawa, Canada, K1P 5S9, May 1996. (Reviewers of ACRP-18 included Arthur
Upton).

It is noteworthy that neither this important paper by William Mayneord
and Roger Clarke (now ICRP chairman and NRPB Director), nor the UNSCEAR
summary of it, have, to my knowledge, been cited or referenced in any
subsequent ICRP or NCRP report  with exception of ICRP 60, page
108-para. B52, (Appendix B).. The citation there is an example of
selective use of the data.

It reads " Generally, high concentrations of radioactive material in
"hot spots" have been found less effective carcinogenically than the
same amount spread uniformly and delivering a lowed but uniform dose.
This, in the main, is in accord with theoretical predictions." (Mayneord
and Clarke, 1973)"
Warren Sinclair was chair of the committee writing Appendix B.


-- 
Wade

mailto:hwade@triax.com

H.Wade Patterson
1116 Linda Lane
Lakeview OR 97630
ph 541 947-4974