Lindex #1281

Hempelmann L, Hall J, Phillips M, Cooper A, Ames R

Neoplasms in Persons Treated with X-Rays in Infancy: Fourth Survey in 20 years.

Journal of the National Cancer Institute

1975; 55(3): 519-530

This is a report of the current status of a 20 year follow-up study conducted primarily by mail questionnaires of radiation-induced neoplasms among 2872 people treated with x-rays in infancy for allegedly enlarged thymus glands. Approximately 5000 non-irradiated siblings of the treated group were also studied. Since the last survey in 1963 (12 years prior) an excess number of neoplasms developed in the thyroid glands and to a lesser extent in blood forming tissues of the irradiated population. Since the numbers of extra thyroid tumors of specific cell types were too small for analysis, only the thyroid neoplasms were studied to determine the effects on tumor induction of age, sex, dose and of being in a high risk group (subgroup C). Subgroup C was treated by a radiologist employing large doses and large sorts resulting in the inclusion of the thyroid gland in the first x-ray beam. In general the irradiated subjects had more than 2X as many malignant and benign tumors (3X increase in incidence) as did the nonirradiated siblings. Almost one-half of the tumors developed in subgroup C, which constituted one-tenth of the irradiated population. This was due first to the increase seen in thyroid cancer seen in subgroup C (13/24 cases). The observed number of thyroid cancer cases in the total irradiated population was almost 100X that expected, whereas that in subgroup C was almost 300X the expectation. By subtraction, the corresponding number of cancer cases not in subgroup C was almost 50X the expectation. The observed number of benign tyroid tumors was also higher than expected. In contrast to the irradiated population, the number of cases of thyroid cancer among siblings was not elevated. Several factors were also analyzed. The ratio of female to male with thyroid neoplasms was determined to be 1.9:1 and 2.3:1 for malignant and benign lesions, respectively. After dose, age and high risk effects were considered, the incidence of cancer in all irradiated females was 2.3X that in males, whereas in 15 to 29 year-old females, the incidence was 5X that of the rest of the irradiated population. In contrast, the incidence in all other females was almost identical with that in males. However, the sex ratio of females to males with thyroid neoplasms was considerably lower than those for thyroid cancer in Upstate New York or for goiter in the normal population.

Next, age effects were studied. It was discovered that the earliest cases were malignant and occurred in boys. Unlike the previous surveys, the new curves for both malignant and benign lesions in the total population indicate that there may be an actual increase rather than a decline in the incidence of these lesions after the treated subjects reach their 20's. Finally, although the curves for incidence vs. age of both thyroid cancer and adenoma increased with age, a multifactor analysis of the data failed to identify a clear proportionality between thyroid neoplasms and age (except in 15-29, female group). The incidence of thyroid cancer was found to be proportional to the dosage, with a linear risk coefficient of 2.5/year/million people exposed to one rad for the entire irradiated.