Imaging Procedures Increase Dialysis Patients’ Cancer Risk

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EEfforts are needed to limit radiation exposure. New research indicates that hemodialysis patients are exposed to unnecessarily high radiation doses that put them at increased risk for the development of cancer (De Mauri A, et al. Estimated radiation exposure from medical imaging in hemodialysis patients. (J Am Soc Nephrol, March 2011). The results add to a growing body of literature suggesting that many patients with chronic and recurrent medical problems receive potentially dangerous doses of radiation from medical imaging.

Too much radiation

Because of comorbidities, many kidney disease patients receiving hemodialysis undergo repeated imaging procedures for both diagnostic and therapeutic purposes that result in repeated exposure to ionizing radiation. This increases their risk for the development of cancer, which is particularly troublesome because maintenance hemodialysis itself is associated with an increased incidence of cancer whose causes are unclear. Therefore, the excess risk of cancer associated with radiation exposure must be taken into careful consideration, particularly in younger patients and in those eligible for kidney transplantation.

To help quantify the extent of that excess risk, Marco Brambilla, PhD, Andreana De Mauri, MD, and their colleagues studied information from a group of 106 hemodialysis patients who were followed up for an average of three years. The investigators retrospectively calculated individual radiation exposures by collecting the number and type of radiologic procedures from hospital records. The goals were to quantify the cumulative effective dose of ionizing radiation in hemodialysis patients, to identify the subgroups that are at increased risk, and to consider the potential health consequences of this radiation exposure.

The investigators found that the mean and median annual cumulative effective doses in the patients in this study were 21.9 and 11.7 mSv per patient-year, respectively. On average, patients received the equivalent of approximately 1000 chest radiographs/year. When stratified by radiation dose, 22 patients were classified as low (<3 mSv/year), 51 as moderate (3 to <20 mSv/year), 22 as high (20 to <50 mSv/year), and 11 as very high (≥50 mSv/year). The annual cumulative effective dose was higher in younger patients and those on transplant waiting lists. This is of particular concern, given the anticipated life expectancy of these individuals and the ongoing use of immunosuppressive agents in waitlisted patients.

The mean and median total cumulative effective doses per patient during the study period were 57.7 and 27.3 mSv, respectively. Seventeen hemodialysis patients had a total cumulative effective dose >100 mSv, which is associated with a substantial increase in risk for cancer-related mortality. Computed tomography (CT) scans accounted for 76% of the total radiation dose but only 19% of the total number of radiologic procedures.

Reducing risk

This research reveals that a significant number of surviving hemodialysis patients during a three-year period receive estimated radiation doses that may put them at an increased risk for cancer. “Although the retrospective nature of this study does not allow us to draw conclusive inferences about the percentage of CT studies that could have been avoided, the significant number of examinations that resulted in non-notable findings or in negative results—about 60%—points toward the need of a more stringent process of justification of CT referral,” said Brambilla.

Others in the field agreed. “We should all—radiologists, nephrologists, and other clinicians—be highly scrutinous of choosing CT or other forms of ionizing radiation in our highest-risk populations. In particular, we should be attentive to our younger hemodialysis patients, since they appear to be most at risk,” said Howard Forman, MD, professor of diagnostic radiology and public health at the Yale School of Medicine in New Haven.

David Brenner, PhD, director of the center for radiological research at Columbia University Medical Center in New York City, said that the article underlines the fact that CT scans should be used only when there is a validated clinical need. But he noted that radiation exposure may be less significant for hemodialysis patients than for many other groups. “This is because the median survival time of dialysis patients is less than the median lag time between radiation exposure and radiation-induced cancer occurrence, which is more than 10 years. So the concern about imaging-related radiation exposure should be pretty low for these folks,” he said.

Steps can be taken to reduce patients’ cancer risk without compromising their medical care, said E. Stephen Amis, Jr., MD, professor and university chair of the department of radiology at The Albert Einstein College of Medicine and Montefiore Medical Center in the Bronx. He noted that many medical conditions, including kidney failure, can be effectively imaged with modalities that do not use ionizing radiation, such as magnetic resonance imaging or ultrasound.

Amis added that physicians who refer patients for imaging, as well as radiologists, need to be aware that total radiation exposure in patients who present again and again with chronic and recurrent conditions can rapidly exceed acceptable levels.

“Radiologists need to act as consultants and not just technicians who perform the exams ordered without question, and referring physicians need to seek and value the consultations provided by radiologists.” He noted that both groups can benefit from the use of guidelines such as the American College of Radiology Appropriateness Criteria, which give a numeric ranking for various imaging examinations that could be used to evaluate a given clinical condition. Amis also recommended that institutions make historical imaging information immediately available to referring physicians when an order for imaging is placed. “Especially effective in the increasingly common electronic physician order entry systems, seeing the imaging history of the patient at that institution when an order is placed for CT will often give pause and result in a different imaging tack,” he said.