Various recently published studies about the relationship between low dose radiation and cancer fanned again the discussion about risk and benefits of modern diagnostic techniques and in particular Computer Tomography (CT). According to an article recently published in IMAGE (Marie H. Meynadier, Vol. 21, no. 10 - March 10, 2008), it is predictable that in a few decades up to 2 percent of cancers in the United States could be linked to the administration of diagnostic x-rays, even if the ability to monitor the increase in cancer related to radiation exposure will be very difficult as radiation-induced cancer can take up to 20 years to develop.

Since many years the relationship between cancer development and radiation exposure has been studied and there are hundreds if not thousands of publications related to this topic. The problem is that a third of all people get cancer anyway, at some time in their lives, and hence it is quite difficult to find evidence that low doses of radiation cause cancers that would not have otherwise occurred. Even for the 80,000 to 90,000 survivors of the atomic bombs exploded over Hiroshima and Nagasaki, exposed to very large radiation doses, it has been hard to find a direct relationship between excess cancer development and radiation exposure. According to Japanese statistics, from the people who were exposed in 1945 (and did not die immediately) nearly half are still alive. A statistically significant increase in cancer was found at relatively high exposure level of 50 millisieverts (mSv is the unit commonly used to measure the effective dose in diagnostic medical procedures), which is about 16 times the current annual average for Americans from medical exams and about 21 times above the average natural background effective dose in the USA. But these numbers need to be analyzed with care. There is a controversy between scientists if levels below 50 mSv can be considered as safe and about the real (and statistically proven) rest-risk of low radiation exposure.

The most widely used mathematical model in estimating radiation risk is known as the linear-nonthreshold dose-respond model. This model assumes that there is no safe dose of radiation and that there is a linear and direct relation between cancer risk and genetic damage with radiation exposure. But this model is in discussion since a long time. For some scientists the linear model is the best way to estimate radiation risk, but for others there exist a threshold below which radiation poses no hazard to health.

It is not difficult to identify the most important sources of man-made or anthropogenic radiation. Most of the collective dose from diagnostic radiology comes from procedures such as CT, interventional radiology and barium enemas. Advances in radiological diagnostic technology have radically transformed medical practice in recent years and there has been a rapid increase particularly in the application of CT. Effective dose estimates of CT scans and nuclear medicine studies are in the range of 10 to 25 mSv for a single study, which is about 100 times larger than those from conventional radiological procedures such as chest x-rays. Although CT scanners contribute to only 12 percent of all medical radiation procedures, the number of CT scans is on the rise. In the United States for instance, no more than 3 million studies using CT were performed in 1980 and in 2006 this number was already above 60 million. Overall, the mean effective dose in the US from all medical x-rays has increased about seven-fold over this period and the situation in Europe is not very different. There are several scientific studies proving a relationship between small radiation doses and cancer formation.

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