ANS National
 Meetings/
 Sessions

June 1995

Robert G. Thomas

(R. Thomas Consult)

1. Radiation is Not Always Harmful to Human Health

“INTRODUCTION

                “TheU.S. populace seems to associate the word radiation synonymously with the word doom. There is good reason for this as the media, special-interest groups, our regulatory agencies, and the ever-present litigious atmosphere exude doom whenever radiation is mentioned. The organizations that establish our radiation guidelines are also at fault as they continue to set levels that are coincident with the mood of the populace.

                “Someof the most extensive epidemiological studies of the effects of ionizing radiation in humans have failed to conclude that there are health effects below whole-body equivalent radiation doses of 0.2 Gy (20 rads). This has been demonstrated in the study of survivors of the bombings in Japan; in the cases of radium dial painters (luminizers) studied in the United States; this value is 10 Gy (1000 rads). The luminizer data comprise the major portion of the discussion in this paper, but it must be emphasized that agency support for this program was severed in 1993, and these valuable data records currently lie unavailable for scientific use.”

“RESULTS AND DISCUSSION

                “Dose-responsedata from the 1515 U.S. female workers who were exposed to radium through the painting of luminous dials and who subsequently had their skeletal burdens measured by whole-body counting and radon breath analyses are lognormally distributed. A lognormal analysis for the 65 cases of radium-induced bone sarcomas and head carcinomas allowed calculation of geometric means and standard deviations for segmented dose populations, and these were used for inter-comparisons of dose responses. The analysis of the radiation dose data from the 65 tumor cases indicates an extrapolated dose of at least 4 Gy below which no skeletal tumors could be expected in a lifetime. An average life time background cancer incidence (0.05%) was subtracted from each calculated point (before division by the dose) to give the final lognormal distributions of the data. The proper background cancer incidence to be used, if there is one, will depend on age at diagnosis, but using the average is a simplistic approach to a problem with large uncertainties. In all tumorigenic categories, negative correlations occur between the total skeletal dose and (a) the age at discovery of a tumor and (b) the time from beginning of exposure to discovery. Thus, the higher the exposure dose, the. lower are the age at tumor development and the length of time to development. This would not necessarily be the case if the age of beginning work had varied over a very large range.   However, only 12% of the female radium dial painters began work after the age of 20 yr. The geometric mean age at beginning of exposure (18 yr) is lower than would be expected today, but these exposures occurred in the 1910s to 1930s. The very strong correlation between latent period and age at death or diagnosis is expected.

                “Mostanalyses of data like that from the radium dial painters use logarithmic axes to express the dose-response because the dose range is very large. The data are lognormally distributed, so this makes log-graphic representation more sensible, even though lognormal presentations can be deceiving. The lognormal analysis does not reflect specific biological processes, but it does verify the existence of a previously reported threshold dose response for ^{226, 228} Rain humans. The term ‘threshold’ in this paper refers to that dose below which no skeletal tumors have been reported. Maletskos et al.¹used hazard function analysis on a similar version of these data and reported a value of 11 Gy as a dose ‘below which radiogenic tumors are estimated statistically not to occur, in support of a threshold  model.’ Evans et al² originally pointed out this no-effect dose as being ~10 Gy to the skeleton, and he referred to it as a ‘practical threshold.’

                “Perhapsmore interesting than the cancer cases are those with radium skeletal burdens that never developed a related illness. The message is that there are 1391female luminizers with average estimated skeletal doses below 10 Gy who have not shown skeletal tumors. This totals to a mean collective dose of ~850person-Gy; assuming a risk for cancer death of 0.01 per person-Gy, this cohort would have been expected to reveal at least five cancer deaths. “

“CONCLUSIONS

                “Theanalysis of the radium luminizer epidemiology study presented demonstrates that it is time to evaluate data objectively instead of formatting an extrapolation scheme before hand and forcing data to fit a preconceived pattern such as linearity through a dose-effect origin. The no-effect dose levels discussed should signal that it is also time to reevaluate (again) the large variations in background radiation levels throughout the world and to cease being concerned with, and regulating against, minuscule doses for which no biomedical effects on humans have ever been satisfactorily identified or quantified.”

1. C. J. MALETSKOS, P. G. GROER, EALGUTIFAN, M. M. SHANAHAN, R. D. EVANS, Health Phys. Suppl. 6, S18 (1992).

2. R. D. EVANS, A. T. KEANE, M. M.SHANAHAN, Radiobiology of Plutonium, p.431, B. J. STOVER, W. S. S. JEE, Eds.,The JW Press, Salt Lake City, Utah (1972).