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Strahlendosis in der Computertomographie

Risiko und Herausforderung

Radiation dose in computed tomography

Risks and challenges

  • Leitthema: Strahlenschutz und MR-Sicherheit
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Zusammenfassung

Die exponentiell zunehmende Leistungsfähigkeit der neuen Scannergenerationen hat zu einer starken Ausbreitung der diagnostischen Möglichkeiten und einem breiteren Einsatz der CT geführt. Den hervorragenden klinischen Eigenschaften der CT steht eine hohe Strahlenexposition gegenüber, die es nötig macht, sowohl die Indikationsstellung als auch die Untersuchungstechnik zu optimieren. Zwar liegt die Strahlenexposition mit modernen Scannern in den meisten Organregionen deutlich unter den diagnostischen Referenzwerten der EU, jedoch ist bei kardialen Untersuchungen eine erheblich höhere Organdosis mit Werten um 100 mGy möglich, für die eine Malignominduktion bewiesen ist. Kritisch ist die Situation auch für Kinder, bei denen bei nicht kindgerechten Scanparametern und schlechter Indikationsstellung die Nutzen-Risiko-Abschätzung nicht immer zu Gunsten der CT ausfällt. Auch der Einsatz bei jungen Patienten, bei Patienten mit guter Prognose und bei häufigen Kontrolluntersuchungen steigert das Risiko für das Individuum und die Bevölkerung. Die Wachstumszahlen der CT-Untersuchungen sind in Deutschland weniger dramatisch als in den USA; dennoch führt die zunehmende Anzahl Scans selbst bei sinkender Dosis pro Untersuchung zu einer Steigerung der Bevölkerungsexposition und einer potenziellen Erhöhung der Malignomrate. Die Kombination von optimalen Scanparametern, automatischer Dosismodulation und Dosisanpassung an den individuellen Patienten kann die Dosis begrenzen. Auch die Reduktion der Scanphasen, Beschränkung der Scanlänge und Wahl einer niedrigen Röhrenspannung kann die Dosis deutlich vermindern. Am wichtigsten ist jedoch die Zusammenarbeit mit den überweisenden Kollegen: Erst wenn die Fragestellung deutlich ist, kann ggf. auf Alternativverfahren ausgewichen werden. Im Hinblick auf die Strahlenexposition wird ein kritischer und sachgerechter Umgang mit dem Verfahren um so wichtiger, je leichter es angefragt wird und je besser die klinischen Ergebnisse werden.

Abstract

The exponentially growing performance of newer scanner generations has increased diagnostic opportunities and utilization of computed tomography. The excellent clinical results with CT, however, have to be weighed against a high radiation exposure. While radiation exposure with modern scanners is well below the diagnostic reference values of the EU for most organ systems, radiation dose for retrospectively gated cardiac examinations can be substantially higher: organ doses can reach 100 mGy, a dose for which cancer induction been proven. For children, the situation may also be critical if scanning parameters are not adapted to their smaller size and increased radiation risk: the risk-benefit ratio may then no longer favor CT. The application of CT for young patients, patients with favorable prognosis and for frequent follow-up examinations will increase the radiation risk to the individual and the population. The growth rates for CT utilization in Germany are well below those in the United States but the increasing number of exams will lead to a substantial increase in population dose even if the dose per individual exam can be reduced. The combination of optimum scanning parameters, automated dose modulation and dose adaptation to the individual patient will help contain radiation dose. Further reduction is possible by reducing the number of scan phases, limiting the scan length and choosing a lower tube voltage. Most important, however, is the close collaboration with referring physicians: scanning technique and choice of imaging modality can only be adapted if the clinical question is clearly defined. In the light of radiation exposure the critical and knowledgeable use of CT becomes the more important the easier it is to request an exam and the better the clinical results.

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Prokop, M. Strahlendosis in der Computertomographie. Radiologe 48, 229–242 (2008). https://doi.org/10.1007/s00117-008-1635-8

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