People with kidney disease requiring dialysis are being routinely exposed to large doses of radiation - the equivalent of 1,000 chest X-rays a year on average - new research shows.
This is putting them at high risk of developing cancer, according to the study published in the Journal of the American Society of Nephrology.
The problem is not dialysis itself, a process used to clean the blood of impurities that involves no radioactive material, but all the tests the patients undergo while being treated.
Marco Brambilla of Maggiore della Carità University Hospital in Novara, Italy said that, most troubling of all, was that the majority of these tests - more than 60 per cent by his calculation - provided no useful information.
The study involved 106 Italian dialysis patients whose medical records were tracked over a three-year period.
Researchers found that patients routinely underwent tests to monitor the health of their kidneys, including intravenous pyelograms (IVP) and computed axial tomography (or CT) scans, both of which use X-rays to produce images of the kidney.
In addition, many kidney patients have other health problems, such as diabetes and cardiovascular disease. As such they will undergo additional tests and procedures such as cardiac perfusion (also known as nuclear stress tests), coronary angiography and percutaneous coronary intervention (more commonly known as angioplasty), all of which involve varying degrees of exposure to low-dose radiation.
Dr. Brambilla found that younger dialysis patients and those on transplant wait-lists were exposed to the largest doses of radiation.
Most of the radiation exposure occurred during CT scans, which expose patients to about 100 times the radiation of a traditional X-ray. While CT scans can be helpful diagnostic tools, they often provide no clinically important information, Dr. Brambilla said.
"These findings emphasize the need to begin tracking at least the CT-related exposure to develop and implement alternative strategies to reduce patient-specific radiation burden," the researcher said.
The rate at which diagnostic tests are performed varies from country to country. In general, though, European doctors tend to order fewer tests than their Canadian counterparts. And Canadian physicians, in turn, order fewer than American doctors. So, Canada occupies the middle ground.
In Canada, about 38,000 people are on dialysis for treatment of kidney failure and the wait-list for a kidney transplant stretches for years. This suggests these patients are undergoing a considerable number of tests that could hike their cancer risk.
In recent years, there has been increasing concern over the cancer risk posed by tests that expose patients to radiation, and a growing number of experts are calling for a registry to track this exposure, particularly in patients with chronic illnesses such as heartor kidney disease.
In an editorial published with the study, David Pickens of the Vanderbilt School of Medicine said procedures like CT scans are too often done without any consideration for the risks.
"Certain types of procedures are overused because they are relatively easy to perform and a large amount of information is provided very quickly," he wrote. "The particular example described here, that of CT scans, can produce substantial cumulative doses of radiation when used multiple times."
Radiation exposure is measured in milliSieverts (mSv) per patient year.
Doses of radiation vary markedly by body part scanned: A kidney disease patient undergoing a CT scan in the abdominal area will be exposed to more than 30 mSv, while someone with a suspected brain tumour will be exposed to as little as two mSV of radiation when the head is scanned. By comparison, a mammography test exposes a woman to a radiation dose of less than one mSv.
A recent study involving Canadian heart patients suggested that cancer risk increased by about 3 per cent for each 10 mSv of exposure to radiation.
A 2009 study published in the Archives of Internal Medicine, estimated that about 2 per cent of all cancers in the United States are caused by exposure to radiation during computed tomography scans.
Researchers estimated that CT scans caused 28,800 cancer cases in the U.S. each year. That total included 14,000 cancers caused by scans of the abdomen and pelvis, 4,100 from chest scans, 4,000 from head scans and 2,700 from CT angiography. Two-thirds of the cancers were found in women.
André Picard