Study links CT scans to hiked cancer risk

Study links CT scans to hiked cancer risk
Yomiuri Shimbun


February 09, 2004



A significant 3.2 percent of Japanese cancer patients are presumed to have developed the disease as a result of their exposure to radiation from radiographic examinations at medical institutions, according to an international study conducted by a group of researchers at Oxford University in England.

The figure is more than three times higher than the average ratio in the United States.

The higher ratio in Japan is "partly because tests involving computerized tomography (CT) equipment are more commonly used than ordinary X-rays in this country," said Takehito Sasaki, a professor emeritus at Tokyo Medical and Dental University, adding that the latter method entails greater doses of radiation.

The findings were revealed by The Lancet, a British medical journal.

The study by the Oxford University group represents an estimate for the numbers of those who have developed cancer in the 15 nations after undergoing X-ray tests, CT scanning and other radiographic tests. The survey covered those aged up to 25.

According to the British group, an average of 7,587 Japanese develop cancer because of their exposure to radiation from radiographic examinations each year. The figure accounts for 3.2 percent of the people who have developed the disease in this country.

This compares with 0.6 percent in Britain nd Poland, 09 percent in the United States and 1.8 percent in Croatia.

According to the latest findings, the number of radiographic tests per 1,000 Japanese stands at a predominant 1,477 annually, 1.8 greater than the average in the 15 countries. The percentage of Japanese who have developed cancer after undergoing radiographic examinations is 2.7 times higher than the average in the 15 nations.

The CT scanning method is used to produce cross-sectional images of patients' organs, using computers to process graphic data taken by X-raying them from various angles.

According to a U.N. report, there are 64 CT units per 1 million Japanese, with Switzerland coming a distant second, with 26 such units.

The CT method was introduced to Japan in 1975. It made it easier to detect cancers at an early stage, and to diagnose cerebral hemorrhages and broken legs.

However, some hospitals have sought to use the method as frequently as possible to collect more medical fees from patients. CT equipment cost between tens of millions of yen to about 100 million yen per unit.

"CT is a workable method. It would be ridiculous to stop using CT equipment out of concern over the latest findings. Doing so could lead to false diagnoses," Sasaki said. "Still, measures should be taken to ensure that doctors use the CT method after fully examining whether there are any alternative methods to examine patients," he said.

Currently, there are no restrictions on the number of CT tests that may be conducted on each patient per year, as well as the number of radiographic images that may be taken of a patient. This means that the dose of radiation to which each patient is exposed depends on what kind of CT equipment is used to examine the patient, as well as how proficient the doctors involved are.

In 2000, the Japan Association of Radiological Technologists compiled a set of guidelines for examinations involving exposure to radiation, setting permissible levels for each organ to be radiographed.

Currently, the association is working to set more rigorous standards. In fiscal 2004, the association also is planning to conduct a survey on CT tests conducted at medical institutions across the nation.

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