February 12, 2009 - In a statement released by the European Society of Radiology (ESR), which will hold its annual meeting, European Congress of Radiology (ECR), in Vienna, March 6-10, 2009, the society stated even when radiation exposure risk to the patient is exceptionally low, and diagnostic benefits outweigh the risk, the doctor should consult with the patient about the necessity of the examination and avoid unnecessary repeat examinations.
Since radiation dosage is dependent on various factors such as the number and thickness of slices or the area to be examined, it is difficult to formulate a generally valid statement regarding radiation exposure for individual patients. Not least of all, tissue sensitivity to radiation also varies widely.
During a CT examination of the skull, a patient is exposed to approximately three millisievert (abbreviated mSv), to approx. seven mSv during a spinal examination while around 20 mSv is listed as an effective dose during an abdominal examination. In general, radiation exposure is much higher than in a “normal” X-ray examination. However, the diagnostic benefits outweigh the radiation risk. Nevertheless, the patient should speak with their doctor about the necessity of the examination and avoid unnecessary repeat examinations. Even when a patient is exposed to relatively low levels of radiation during an examination, this should not be disregarded. Due to findings about the effects of weak, high-energy ionizing radiation (such as X-rays) on humans, one can assume that the resulting risk to the patient is exceptionally low. One must compare the radiation risk to the risk that can result from an examination not carried out, such as the spreading of a tumor due to a false assessment.
CT delivers good images of almost all body regions and tissues. Applications in cancer diagnosis are primarily the visualization of the brain as well as the breast, abdomen and pelvic organs. For example, liver metastases one to two centimetres in size are visible with CT. The simpler ultrasound examination is also exceptionally well suited, but its capacity depends largely on the skill of the examining doctor and the corporal constitution of the patient. Its effectiveness can be very limited, for example in extremely overweight patients. Lesions in the pancreas, in the rear abdominal cavity, kidneys and pelvis can be detected with a high degree of precision. Computed tomography is also well suited in the detection of tumors in the chest cavity.
In post-examinations of various cancer diseases, CT can also be useful. Examinations can serve as therapy progress assessments and can clarify the suspicion of renewed tumour growth.
Concerns have been raised regarding the increasing use of CT examinations on patients without symptoms for early detection of diseases. Up to now, the benefits of such examinations have not been scientifically verified. If the benefits are unknown, then the risk of radiation from such examinations carries a more significant weight.
The number of x-ray examinations slightly decreased over the period from 1996 to 2004. About one-third of the examinations were carried out in the dental sector. The radiation dose per resident and year, however, increased over the same period by 15 percent. This is significant, since radiation exposure without CT examinations would have decreased by 15 percent. The cause for the dosage increase in this period is the sharp increase in CT examinations of over 60 percent. By international comparison, it is significant that primarily in England especially few CTs per resident and year are carried out. The average radiation exposure per CT examination is relatively low with 6 mSv. Four times as many CTs were carried out in Germany and 10 times as many in Japan.
Cancer patients undergoing X-ray checkups in Germany make up less than 1 percent of the total population, but receive an estimated 15-20 percent of the radiation dose used per year. Due to older age and yet limited life expectancy, radiation exposure for this group is in many cases irrelevant in the context of radiation biology. Sievert (Sv) refers to the dosage that considers not only the type of radiation and radiation conditions, but also the various radiation sensitivity of the affected tissue and organs. In comparison: the average natural radiation exposure per resident in Germany is about 2.1 mSv.
Besides CT, there are other imaging examination methods like X-ray, ultrasound and MRI. Which examination method is used or which provides a better diagnostic assessment depends on the problem to be evaluated and the body region to be examined and must therefore be decided on an individual basis. However, CT, X-ray, ultrasound and magnetic resonance imaging cannot be applied and exchanged at will.