A recent study that shows an estimated 3.2 percent of cancer cases in Japan were caused by exposure to radiation during radiographic examinations at hospitals serves as a warning to medical authorities that such examinations are conducted too frequently.

Although concerns that patients could develop cancer from radiographic examinations have existed for a long time, the study by a research group at Oxford University in Britain is the first of its kind to compare data from 15 countries.

According to the study, Japan's figure is the highest among the 15 countries and is more than five times higher than that of Britain. Although the figure is an estimate, medical authorities were astonished.

A possible reason for Japan's high cancer risk is thought to be high accessibility to computerized tomography (CT) equipment.

Only large hospitals have the equipment in most Western countries, but hospitals in Japan, including those in rural areas, have approximately 8,000 CT scanning machines, which is far more than in any other country.

Thanks to CT scanning machines, which can take images of very tiny lesions that cannot be found by ordinary X-ray machines, there has been phenomenal progress in diagnosing cancer, cerebral hemorrhage and fractured bones.

But patients are exposed to a substantial amount of radiation when undergoing CT scanning tests. On average, a patient is exposed to at least several hundred times more radiation in a CT test than in a chest X-ray examination, although the result depends on scanning circumstances.

No limitation has been set as to how much radiation can cause cancer, and it is said that the risk of developing cancer by undergoing a single CT scan is small.

The more radiation you are exposed to, however, the more likely you are to develop cancer. Perhaps doctors should inform patients not only of the merits of having a CT scan done, but also of the risk involved.

What really matters is deciding whether CT scans are really necessary to diagnose each case and trying to keep the amount of radiation at a minimum. In many cases, however, medical institutions are inclined to use CT equipment too readily.

Masaomi Ikusaka, a professor at Chiba University's medical department, said that, in the case of a patient with a headache, for example, it is often possible to discern whether the patient needs a CT scan or not by asking him or her whether the pain started suddenly or increased gradually and by carefully examining the patient's physical condition.

'There are only a handful of patients who need CT scan. At some medical institutions, however, most of the patients who claim to have headaches undergo CT scan,' Ikusaka said.

Behind this practice lies the fact that there are doctors who rely on test equipment because they lack the ability to diagnose a patient by interviewing him or her or by other methods.

It is medical education that produces such doctors. Practical training of medical students and trainee doctors is mostly done in hospital wards, leaving many of those students and trainee doctors without opportunities to examine outpatients.

There is a difference between examining a new outpatient and an inpatient who has already been diagnosed. Examining outpatients is important in training diagnostic techniques, but such training is said to be rare in Japan.

'In the West, trainees can improve their ability to figure out what kind of tests each patient needs in a hospital's outpatient ward or at a practicing doctor's surgeon. In comparison, the situation isn't good enough in Japan,' Ikusaka said.

There is also the issue of medical service fees. Fees for one interview are the same no matter how much time a doctor spends asking questions. But the more examinations a patient receives, the more revenue a doctor or a hospital can generate.

Unlike the United States, where insurance companies strictly check medical examinations to see whether they are really necessary, doctors and hospitals here can schedule them at will.

Some patients are also to blame. The presence of a CT scanner has become a selling point for hospitals, suggesting that patients also request CT scans to allay their fears.

In addition, CT scans have become defensive moves for some hospitals, who fear lawsuits in the case of misdiagnoses. If they have not performed a CT scan, it works to their disadvantage.

In the Oxford University report, Britain had the lowest number of radiodiagnoses and the lowest rate of cancer. In Britain, there are guidelines that suggest which examinations should be done for certain diseases, which contributes to cutting down the number of unnecessary tests.

In Japan, it was only last autumn that specialist organizations in radiology drew up guidelines for diagnostic imaging, which have not spread widely enough.

Moreover, the dose of radiation a patient is exposed to in the same CT examinations differs from hospital to hospital, as not all medical institutions are aware that they should keep the amount of radiation to a minimum.

In 2000, the Japan Association of Radiological Technologists set ceilings on how much radiation a patient should be exposed to in different examinations. The association should discuss releasing the names of medical institutions that breach these ceilings.

Patients, too, should avoid having multiple radiographic examinations by taking their records when changing hospitals or asking for a second opinion from a doctor other than their primary physician.

The role of radiographic examinations, including CT scanning, will remain important in modern medicine. To maintain trust in the method, medical authorities should establish a system to use it correctly.