13 februari 2012: ik heb de link naar het artikel uit The Lancet waarop commentaar wordt gegeven hersteld.
Twee Duitse Radiologen geven in een artikel in the Lancet commentaar op studie zoals gepubliceerd in The Lancet d.d. 31 januari 2004: vol. 363 p. 345:
Risk of cancer from diagnostic X-rays
The role of diagnostic X-rays has evolved from classic conventional radiography and uniform thickslice CT to highly specialised imaging, which has the potential to reduce the overall radiation exposure of individuals undergoing the examination and has better diagnostic accuracy. However, there is no threshold of radiation dose under which the absence of any cancer risk is proven.1 On the other hand, there are no reliable data proving that radiation doses as used in diagnostic X-rays do induce cancer.2
In today's Lancet, Amy Berrington de González and Sarah Darby use cancer-rate data from survivors of the Japanese atomic bombings as a model to study the risk of cancer from diagnostic X-rays. These researchers compiled their data on the incidence of cancers from tumour registers in the UK and 14 other countries. They compared these cancer rates with the numbers of X-ray procedures done in these countries and statistically analysed the number of cancers induced by the radiation exposure from these procedures. The lifetime risk of developing cancer attributable to diagnostic X-rays was 0·6-1·8% in the countries investigated, except in Japan, where the lifetime risk was 3·2%. In the UK, for example, this exposure causes an annual excess risk of 700 cancer cases.
The Japanese survival data are the best available because there are no other data showing the effect of ionising radiation on a large human population; but the data have limitations. One limitation is that the survivors were not only directly exposed with rays from the bomb detonations but also with ßradiation, and, most importantly, by incorporation of radionuclides emitting ßand high-energy radiation from contaminated food, water, and dust in the air. This additional exposure will not occur in patients undergoing radiological examinations but contributes to the morbidity and mortality of the atomic bomb survivors. Additionally the rays to which the atomic bomb survivors were exposed were of a different energy spectrum from that used for diagnostic X-ray. Without better data, however, it is probably adequate to use the Japanese data. But these additional concerns should be taken seriously and the derived numbers for the incidence of cancer caused by X-rays should be critically assessed in future investigations, because the cancer risk is probably overestimated with use of the Japanese data.
The Japanese data were collected between 1991 and 1996. In recent years, at least in Germany and the USA, the number of CT examinations has steadily increased by up to 30% a year while conventional radiography has decreased.3 CT generally leads to a higher exposure with X rays than conventional radiographs of the same section of the body, although the exposure is more dependent on the scanner and exposure parameters than with conventional X rays.4,5 The possible increase of radiation exposure by more extensive use of CT awaits study.
There are differences between countries in how CT parameters are set.3,6 In the USA, exposure parameters are generally set to achieve much higher doses (to reduce image noise) than in Europe, where there is a higher emphasis on reducing the radiation exposure of patients. In some countries, governmental authorities control the radiological exposure of patients and restrict the radiation doses for each kind of examination.7
Strategies and techniques to reduce radiation dose during CT, such as real-time dose-modulation,8-11 are effective but not used in every country in the same way.12 These special techniques are usually only used in newer generations of scanners, which are mostly installed in richer countries.
The upcoming widespread use of digital and digital luminescence (flat panel) radiography means that patients undergoing conventional radiography will be exposed to substantially less radiation.13 Digital radiography with post-processing reduces the number of repeat exposures required because of over-exposure or overblending.
Berrington de González and Darby did not assess the indications or benefits achieved for patients in X-ray examinations. Benefits include the earlier detection of cancers by radiological examinations and the possibility of early treatment, which probably allows more cure of cancers than radiological exposure is able to cause.
A general goal must be to avoid unnecessary X-ray procedures. Up to 30% of chest X-rays may not be indicated;14 unnecessary CT examinations can lengthen hospital stay15 as well as causing radiation exposure. In everyday practice, those ordering radiological procedures should think carefully about the benefit for and the risk to their patients for each examination.
We have no conflict of interest to declare.
*Peter Herzog, Christina T Rieger
Institute of Clinical Radiology (PH) and Department of Internal Medicine III, Hemato-Oncology (CTR), Ludwig-Maximilians-University Munich, D-81377 Munich, Germany (e-mail: firstname.lastname@example.org )
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13 Bacher K, Smeets P, Bonnarens K, De Hauwere A, Verstraete K, Thierens H. Dose reduction in patients undergoing chest imaging: digital amorphous silicon flat-panel detector radiography versus conventional film-screen radiography and phosphor-based computed radiography. AJR Am J Roentgenol 2003; 181: 923-29.
14 McCreath GT, O'Neill KF, Kincaid WC, Hay LA. Audit of chest X-rays in general practice--a case for local guidelines? Health Bull (Edinb) 1999; 57: 180-85.
15 Fleszler F, Friedenberg F, Krevsky B, Friedel D, Braitman LE. Abdominal computed tomography prolongs length of stay and is frequently unnecessary in the evaluation of acute pancreatitis. Am J Med Sci 2003; 325: 251-55.
- Commentaar op studie over risico van bestraling (X-rays) zoals blijkt uit studie van onderzoekers aan de universiteit van Oxford
- Scans en ook foto's bij de tandarts veroorzaken honderden nieuwe gevallen van kanker per jaar alleen al in Engeland en duizenden doden door kanker wereldwijd aldus studie aan universiteit van Oxfort