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The objective of the study is to characterize the risk of tumors from radiation exposure to the head and neck. A cohort of 2,224 children given x-ray treatment and 1,380 given only topical medications for ringworm of the scalp (tinea capitis) during 1940–1959 have been followed up for a median of 39 y to determine tumor incidence. Follow-ups were by mail/telephone questionnaire, with 84–88% of the original cohort followed and with medical verification of diseases of interest. Sixteen intracranial tumors [7 brain cancers, 4 meningiomas, and 5 acoustic neuromas (vestibular schwannomas)] occurred in the x-irradiated group following an average brain dose of about 1.4 Gy, compared to 1 acoustic neuroma in the control group. The standardized incidence ratio (SIR) for brain cancer was 3.0 [95% confidence interval (CI): 1.3, 5.9]. Even though the dose to the thyroid gland was only about 60 mGy, 2 thyroid cancers were found in the irradiated group vs. none among controls, and 11 vs. 1 thyroid adenomas were found in the respective groups. Following an average dose of about 4 Gy to cranial marrow, 8 cases of leukemia (SIR = 3.2, CI: 1.5, 6.1) were observed in the irradiated group and 1 in the control group. There was also a suggestive excess of blood dyscrasias. There was no difference between the groups in the frequency of other cancers of the head and neck (excluding nonmelanoma skin cancer) or in total mortality.