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W K Sinclair

Publications and source records attributed to W K Sinclair.

At least 19 recordsLinked to original sources
PubMed1998

The linear no-threshold response: why not linearity?

ICRP and NCRP recommend risk coefficients for use in radiation protection that are based on a linear quadratic response in the low dose region. This is a derivative of the linear no threshold (LNT) hypothesis with allowance for low dose and dose rate effects. The risk coefficients are derived from the Lifespan Study of the A-bomb survivors but are supported by many other epidemiological studies some, such as occupational, at low doses. Nevertheless, the risk coefficients are uncertain and range (90% confidence intervals) over a factor of 2-3 above and below the nominal values. Various possible dose responses in the low dose region are considered including those that may result from adaptive responses. Laboratory studies show linearity in some systems to doses as low as 2.5 mGy. Epidemiological studies include several with significant excess risks at 100 mGy or less with at least one at 10 mGy. The linear quadratic response seems, therefore, the most likely response in the very low dose region. Adopting the linear quadratic response in the low dose region does not prevent common sense judgements about dismissing small radiation risks. NCRP defined first a negligible individual risk (1987) and then an individual dose (1993) to encourage common sense judgements in the low dose region. More consideration might be given to dismissing minor risks in common sense applications in radiation protection.

Data Interpretation, Statistical↗
PubMed1996

The present system of quantities and units for radiation protection.

The International Commission on Radiation Units and Measurements has over the last decade developed operational quantities, the ambient, directional and personal dose equivalent, suitable for the measurement of radiation fields in a variety of circumstances. Experience with the use of these quantities to represent the dose limitation quantities defined by the International Commission on Radiological Protection in 1977 has been an important part of recent radiation protection metrology. The definition by International Commission on Radiological Protection in 1991 of new limitation quantities, the equivalent dose and the effective dose has necessitated a redirection of this work. The metrology field has made good progress, however. It has found that for photons, at least above 50 keV, the effective dose can be measured by the ambient dose equivalent about as well as the former effective dose equivalent. Unfortunately, for neutrons the existing and already quite severe complications have been made somewhat worse by the new quantities although not any worse in the important region between 0.1 and 1 MeV. Neutron measurements over a broad energy range are the subject of extensive evaluation and some new suggestions as the metrology field wrestles with these problems. Values of wR constitute an important part of the International Commission on Radiological Protection recommendations. A brief history of the development of higher relative biological effectiveness values for fission neutrons and alpha particles leading to the selection of 20 for wR in each case, is provided.

Dose-Response Relationship, Radiation↗
PubMed1995

Radiation protection recommendations on dose limits: the role of the NCRP and the ICRP and future developments.

The purpose of this paper is to review the role of the National Council on Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP) in making recommendations on dose limits for ionizing radiation exposure for workers and for the public. The text describes the new limits for workers and public recommended by ICRP in 1991 and NCRP in 1993 and the composition of the radiation health detriment on which they are based. The main component of this detriment is the risk of radiation induced cancer which is now estimated to be about three times greater than a decade or so earlier. Uncertainties in these risk estimates are discussed. Some special radiation protection problems, such as those for the embryo or fetus are described. The article also addresses future progress in radiation protection particularly with regard to future improvements in the scientific basis for radiation protection recommendations.

Environmental Exposure↗
PubMed1990

The 1986 and 1988 UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) reports: findings and implications.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has published a substantive series of reports concerning sources, effects, and risks of ionizing radiation. This article summarizes the highlights and conclusions from the most recent 1986 and 1988 reports. The present annual per person effective dose equivalent for the world's population is about 3 mSv. The majority of this (2.4 mSv) comes from natural background, and 0.4 to 1 mSv is from medical exposures. Other sources contribute less than 0.02 mSv annually. The worldwide collective effective dose equivalent annually is between 13 and 16 million person-Sv. The Committee assessed the collective effective dose equivalent to the population of the northern hemisphere from the reactor accident at Chernobyl and concluded that this is about 600,000 person-Sv. The Committee also reviewed risk estimates for radiation carcinogenesis which included the new Japanese dosimetry at Hiroshima and Nagasaki. These data indicate that risk coefficient estimates for high doses and high dose rate low-LET radiation in the Japanese population are approximately 3-10% Sv-1, depending on the projection model utilized. The Committee also indicated that, in calculation of such risks at low doses and low dose rates, a risk-reduction factor in the range of 2-10 may be considered.

Accidents↗
PubMed1988

Trends in radiation protection--a view from the National Council on Radiation Protection and Measurements (NCRP).

The present status of ionizing radiation protection in our society, with the exception of extraordinary events such as the Chernobyl accident, can be considered reasonably satisfactory. Occupationally, average exposures have risks no greater than accident rates in "safe" industries and show a downward trend in concert with results of safety practices in other occupations; higher exposures are being addressed specifically, and a new NCRP guideline may prove useful. An important concern relating to the quality factor for neutrons is at least partially accounted for by recent International Commission on Radiological Protection (ICRP) and NCRP recommendations. Among public exposures, the most important by far is exposure to indoor Rn. However, this problem is being addressed on all fronts, and its magnitude and the means to deal with it will soon be better known. For the near future, we should see a stabilizing of risk estimates, albeit at levels very probably higher than formerly. There may also be an increasing tendency to use incidence rather than mortality for calculating these estimates. These changes may require some adjustment in our perspective on limits. As the difference in risk between the sexes becomes more definite, we may wish to adopt a policy of equal risk rather than one of equal dose. Age data also emphasize, more and more, the decline of risk with age; consequently, using older workers when feasible in radiation-exposure circumstances becomes more desirable. For the longer-term future, various developments can be expected, including, possibly, a more suitable climate for a risk system, a more appropriate way to express differences in radiation quality, further knowledge of the role probabilities of causation may play in radiation control, the effect of mitigating and enhancing factors, and progress in fundamental oncology. All of these are exciting possibilities which may provide a variety of options for the most effective radiation protection in the future.

Accidents↗
PubMed1987

New dosimetry of atomic bomb radiations.

The reassessment of the radiation dosimetry from the Hiroshima and Nagasaki atomic bombs is almost complete. Since atomic bomb survivors provide a major source of data for estimates of risk of cancer induction by radiation the impact of the new dosimetry on risk estimates and radiation protection standards is important. The changes include an increase of about 20% in the estimated yield of the Hiroshima bomb and a reduction in the estimated doses from neutrons in both cities. The estimated neutron dose for Hiroshima is about 10% of the previous estimate. The neutron doses are now so small that direct estimates of neutron relative biological effectiveness may be precluded or be much more difficult. There is little change in most of the gamma ray organ doses because various changes in the new estimates tend to cancel each other out. The new estimate of the attenuation of the free-in-air kerma by the walls of the homes is about twice that used in the previous dosimetry. But the transmission of gamma radiation to the deep organs such as bone marrow is significantly greater than earlier estimates. Probably future risk estimates for radiogenic cancer will be somewhat higher because of both the new dosimetry and the new cancer mortality data. New risk estimates should be available in 1988.

Brain↗
PubMed1987

Failla memorial lecture. Risk, research, and radiation protection.

Radiation protection concerns the risk of stochastic late effects, especially cancer, and limits on radiation exposure both occupationally and for the public tend to be based on these risks. The risks are determined, mainly by expert committees, from the steadily growing information on exposed human populations, especially the survivors of the atomic bombs dropped in Japan in 1945. Risks of cancer estimated up to the early 1980s were in the range 1 to 5 X 10(-2)/Sv, but recent revisions in the dosimetry of the Japanese survivors and additional cycles of epidemiological information suggest values now probably at the high end of this range. These are likely to require an increase in the values used for radiation protection. A major problem with risk estimation is that data are available only for substantial doses and must be extrapolated down to the low-dose region of interest in radiation protection. Thus the shape of the dose-response curve is important, and here we must turn to laboratory research. Of importance are studies involving (1) dose rate, which affects the response to low-LET radiation and often to high-LET radiation as well; (2) radiation quality, since the shapes of the dose-response curves for high- and low-LET radiation differ and thus the RBE, the ratio between them, varies, reaching a maximum value RBEM at low doses; and (3) modifiers of the carcinogenic response, which either enhance or reduce the effect of a given dose. Radiation protection depends both on risk information, and especially also on comparisons with other occupational and public risks, and on research, not only for extrapolations of risk to low doses but also in areas where human information is lacking such as in the effects of radiation quality and in modifications of response.

Animals↗
PubMed1981

Effects of low-level radiation and comparative risk.

At low doses of radiation to the whole body, the dose-effect relationship for human must usually be determined by extrapolation from human data at high doses. Reasons for above-linear, linear, or below-linear extrapolation from high doses to low doses are discussed. The linear extrapolation is most common, and probably leads to conservative estimates of risk. Risks from other carcinogens may be compared directly with radiation risk by using cancer incidence as the end point. However, lifeshortening is a more useful index of comparison in many other circumstances, and can be used to compare the time lost due to radiation-induced cancer with that due to accidental deaths and other lost industrial time. Risks for radiation workers exposed at current average occupational dose levels are shown to be comparable with those from other safe industries. Questions of acceptability and public perception of risk are briefly discussed.

Accidents, Occupational↗