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Etiology

The cumulative diagnostic radiograph dose was not associated with leukemia or lymphoma but was weakly associated with multiple myeloma

ACP J Club. 1991 July-Aug;115:28. doi:10.7326/ACPJC-1991-115-1-028


Source Citation

Boice JD Jr, Morin MM, Glass AG, et al. Diagnostic x-ray procedures and risk of leukemia, lymphoma, and multiple myeloma. JAMA. 1991 Mar 13;265:1290-4.


Abstract

Objective

To find whether a diagnosis of leukemia, lymphoma, or multiple myeloma among adult clients of prepaid health plans is related to radiation exposure from diagnostic radiograph examinations.

Design

Case-control study.

Setting

Patient records of 2 health plans from 1959 to 1979 in Oregon and from 1956 to 1982 in northern California.

Patients

The diagnostic radiograph exposure of adults with leukemia, non-Hodgkin lymphoma, or multiple myeloma was compared with matched controls. 565 patients with leukemia, 318 patients with non-Hodgkin lymphoma, 208 patients with multiple myeloma, and 1390 controls were studied. Median age of entry into the health care plans was 45 years; more than 60% of the patients were men.

Assessment of risk factors

Diagnostic radiograph procedures were extracted from records masked to case or control status and assigned a value for the probable dose to the active bone marrow. The cumulative dose for each patient was summed from the number of procedures done. The number of high-exposure radiographs included was calculated. The time lag between the procedure and the diagnosis of cancer was noted.

Assessment of outcome

Histologically supported diagnoses were extracted.

Main results

52% of the 25 421 radiographs taken were chest roentgenograms; the mean number of procedures per patient was 11.6; 12% of exposures were high-dose fluoroscopic or multifilm procedures. Patients with chronic lymphocytic leukemia showed a trend toward having had fewer radiograph procedures than their controls; excluding exposures within 5 years of diagnosis, the relative risk was 0.51 (95% CI 0.3 to 0.9, P < 0.05). For other leukemias and for non-Hodgkin lymphoma, no differences were found between the groups in mean exposure scores. A trend existed toward an association between increasing radiograph exposure and risk for multiple myeloma (P for trend = 0.05), particularly when patients were excluded whose radiograph procedures were done more closely to the diagnosis.

Conclusions

The cumulative dose from diagnostic radiograph procedures was not associated with a diagnosis of leukemia or lymphoma. A trend existed toward a radiograph dose-related development of multiple myeloma, particularly when exposures within 2 years of the diagnosis were excluded.

Source of funding: In part, National Cancer Institute.

Address for article reprint: Dr. J.D. Boice, Radiation Epidemiology Branch, National Cancer Institute, 6130 Executive Boulevard, Executive Plaza North, Room 408, Bethesda, MD 20852, USA.


Commentary

The best estimates of risk from acute radiation exposure have come from studies of persons who survived an atomic-bomb (1). Extrapolating these data to estimate cancer risk from diagnostic radiograph procedures has probably been inaccurate because of the multiple exposures over time to lower doses of radiation. The few studies that addressed exposure to diagnostic radiograph procedures produced conflicting results.

The present well-designed, case-control study is a valuable contribution to this literature and corrects some of the deficiencies of previous reports. Because the patients were members of a prepaid health plan, the authors were able to account for virtually all radiologic investigations, eliminating any recall bias. They carefully matched the cases to controls and appropriately excluded exposures close to the diagnosis of cancer. Although it is the largest study of its type, interpretation of the negative results would have been enhanced by a power calculation.

Although the reported lack of association between diagnostic radiograph exposure and leukemia is reassuring, we must not conclude that diagnostic radiograph procedures are completely safe. This study still addresses only a short-term exposure to a carcinogen that has a long latency. In survivors of an atomic bomb, the excess incidence of multiple myeloma did not become detectable until 20 years after irradiation (1). Because only one third of study patients were followed for more than 15 years, the near-significant relation between radiograph exposure and multiple myeloma is of particular concern. Larger studies with longer follow-up are needed before we can be sure that diagnostic radiography is as safe as these short-term data suggest.

Thomas G. Tape, MD
University of Nebraska Medical CenterOmaha, Nebraska, USA


Reference

1. National Academy of Sciences, National Research Council. Health Effects of Exposure To Low Levels of Ionizing Radiation: The Committee on the Biological Effects of Ionizing Radiations (BIER V). Washington, DC: National Academy Press; 1990.