Radiogenic Risk Research Articles

On the relationship between radiation standards for the general public and limitation of lifetime risk.

This paper discusses the relationship between standards for limiting radiation exposures of individuals in the general public and limitation of lifetime risk. Most current radiation standards for the public in the United States specify limits on dose for each year of exposure. Particularly for internal exposures, we show that such standards may correspond poorly with a limit on lifetime risk when the age dependence of radionuclide intakes and dose is taken into account. We then show that standards which specify limits on annual dose averaged over a lifetime, with a subsidiary limit on dose in any year, correspond more closely with a limit on lifetime risk. Finally, we discuss standards for public exposures that are expressed directly as limits on lifetime risk. The development of risk standards would require consideration of age-dependent radiogenic risks and competing risks from all other causes as well as age-dependent dosimetry. We present sample calculations of lifetime risks from acute and chronic intakes that would support such a standard. We suggest that implementation of a standard for lifetime risk would require modification or abandonment of several radiation protection practices embodied in standards which specify limits on dose.

A Population-Based Case-Control Study of Thyroid Cancer

A population-based case-control interview study of thyroid cancer (159 cases and 285 controls) was conducted in Connecticut. Prior radiotherapy to the head or neck was reported by 12% of the cases and 4% of the controls [odds ratio (OR) = 2.8; 95% confidence interval = 1.2-6.9]. Risk was inversely related to age at irradiation and was highest among children exposed under age 10. Few persons born after 1945 received prior radiotherapy, consistent with the declining use of radiation to treat benign conditions in the 1950's. Among females the radiogenic risk appeared to be potentiated by the number of subsequent live-births. Other significant risk factors included a history of benign thyroid nodules (OR = 33) or goiter (OR = 5.6). Miscarriage and multiparity increased risk but only among women who developed thyroid cancer before age 35 years. Consumption of shellfish (a rich source of iodine) seemed to increase the risk of follicular thyroid cancer, whereas consumption of goitrogen-containing vegetables appeared to reduce risk of total thyroid cancer, possibly because of their cruciferous nature. A significantly low risk was observed among persons of English descent, whereas Italian ancestry appeared to increase risk. No significant associations were found with a number of suspected risk factors: diagnostic x-rays, radioactive isotope scans, occupational radiation exposure, tonsillectomy, Jewish ethnicity, alcohol intake, cigarette smoking, oral contraceptives, lactation suppressants, menopausal estrogens, most other common medications, and water source. New associations were suggested for obesity among females (OR = 1.5), surgically treated benign breast disease (OR = 1.6), use of spironolactone (OR = 4.3) or vitamin D supplements (OR = 1.8), and a family history of thyroid cancer (OR = 5.2). About 9% of the incident thyroid cancers could be attributed to prior head and neck irradiation, 4% to goiter, and 17% to thyroid nodular disease, leaving the etiology of most thyroid cancers yet to be explained.

Cancer Mortality After Multiple Fluoroscopic Examinations of the Chest2

Total cancer deaths were not increased among 2,074 women and 1,277 men who were fluoroscopically examined an average of 73 and 91 times, respectively, during lung-collapse therapy for tuberculosis (TB). Patients who did not receive this form of therapy (2,141 women and 1,418 men) and general population rates were used for comparison. All subjects were discharged alive from eight TB sanatoria in Massachusetts between 1930 and 1954; the average follow-up was 23 years. Deaths due to breast cancer were not increased among exposed females [standardized mortality ratio (SMR) = 1.0, n = 24], and SMRs greater than 2.1 could be excluded with 95% confidence. In contrast to other series, our inability to detect a breast cancer excess was likely due to lower breast doses (66 rad) and higher average ages at exposure (28 yr) and thus lower sensitivity. A deficit of lung cancer among exposed males and females was observed (SMR = 0.8, n = 26), even though increased risks have been observed among other populations exposed to similar dose levels. The estimated average lung dose was 91 rad, and SMRs greater than 1.2 for lung cancer could be excluded with 95% confidence. Overall, this study indicates that the radiation hazard of multiple low-dose exposures experienced over many years is not greater than currently accepted estimates for breast and lung cancer. For lung cancer the radiogenic risk may be less than predicted from high-dose, single-exposure studies.

Some recent statistical analyses of two long-term studies of exposure to ionizing radiation.

Two long-term studies of cancer mortality in population exposed to high doses of ionizing radiation are described briefly. Statistical analysis plays a key role in establishing to what extent it is appropriate to generalize from the experience of these populations to that of other populations who have been exposed, usually at lower doses. Two examples of recent analyses are given. First, a detailed comparison of the cancer mortality experience in the two studies has been carried out; this has shown a high level of agreement between them. In the second example the relation between the radiogenic risk and the baseline age-specific cancer risk in the two populations has been studied. Results are again in good agreement and show that for a group of epithelial tumours of non-sex-specific sites exposure to radiation multiplies the baseline risk.

Thyroid Tumors Following Thymus Irradiation<xref ref-type="fn" rid="FN2">2</xref>

About 2,650 persons who received X-ray treatment for purported enlarged thymuses in infancy and 4,800 sibling controls have been followed by mail questionnaire for an average of 29 years to observe their incidence of thyroid tumors. The follow-up rate in the latest survey was 88% in both groups. The radiation doses to the thyroid gland ranged from 5 to over 1,000 rad, with 62% receiving less than 50 rad. To date 30 thyroid cancers and 59 benign thyroid adenomas have been detected in the irradiated group, as compared with 1 thyroid cancer and 8 adenomas in the control group. The relative risks in the irradiated group were about 45 for thyroid cancer and 15 for benign thyroid adenomas. The dose-response curve for thyroid cancer was essentially linear, although a linear-quadratic curve could not be ruled out. For thyroid adenomas the risk per rad was somewhat greater at lower doses than at high doses. For both thyroid cancers and adenomas the absolute excess risk per rad was two to three times as great in females as males. Within the limitations imposed by the treatment regimens and the sample size, there was no indication of a "sparing" effect due to dose fractionation for either thyroid cancers or adenomas. There was an excess risk for both malignant and benign thyroid tumors for at least 40 years post irradiation. For thyroid cancer the radiogenic risk appeared to be additive with respect to time, rather than the age-specific natural rates of cancer being multiplied.

Truth and Meaning in the Determination of Radiogenic Risk

Let me start with the assumption that the reader is concerned with determining the risk imposed by human exposure to radiation. These exposures might occur, for instance, in the routine operation of a radiotherapy unit or in some phase of testing a radio-labeled pharmaceutical. The question I want to address concerns the extent to which anyone engaged in the approval of such activities can base his or her opinions and decisions on firmly logical grounds. In other words, in assigning a level of risk to be expected from a given exposure to radiation, when should we feel that past experience dictates an answer and when should we admit that estimates contain significant judgments that might differ among people? While I can offer no final answer to this question, I shall explore the features of such an answer by examining a distinction between truth and meaning in science. One method for dealing with problems requiring a great deal of scientific expertise is to seek the opinions of the scientific community. Acting on the basis of estimates provided by a scientific expert involves accepting the best judgments made by people who have carefully examined the past. The idea is that all reasonable people, if only they had the time and training to examine the scientific evidence, would arrive at identical scientific judgments. Scientists do not, however, come to the same judgments based on past experience. They differ in their interpretations, leaving an IRB with the problem of determining which judgment the members themselves would have arrived at if they had been able to deal directly with the evidence. I intend to explore this problem in this article and to come to some understanding of why scientists differ in their judgments. I intend also to develop a set of ideas, arising from epistemology, which the layperson can use in examining these differences. I hope to show that risk estimates put forth by individual scientists involve selecting one possible interpretation from a rather large group of perfectly valid interpretations of experience. This process of selection should not be expected to be the same in all people, for it will depend on a judgment of the possibility, and consequences, of incorrect selection. While weighing the risks and benefits of an action will probably remain a purely personal judgment, it is currently possible to deal explicitly with the problem of competing estimates of those risks.

Dose reduction in xeromammography (author's transl)

The use of a total filter of 3 mm of aluminium permits a considerable reduction of the radiation dose in xeromammography using the senographe. In comparison with conventional xeroradiography radiation is reduced by a factor of 2 to 3, in comparison with foilless film by a factor of 10 to 12. The applied tissue dose is between 0.14 and 0.30 rad per exposure. The presently still hypothetic radiogenic risk of carcinoma due to mammography is thus lower for this system than with other systems. The quality of the radiograph and the diagnostic validity are not reduced by this technique.