Prenatal Radiation Exposure: Dose Calculation

Abstract

The unborn child requires special protection. In this context, the indication for an X-ray examination is to be checked critically. If thereupon radiation of the lower abdomen including the uterus cannot be avoided, the examination should be postponed until the end of pregnancy or alternative examination techniques should be considered. Under certain circumstances, either accidental or in unavoidable cases after a thorough risk assessment, radiation exposure of the unborn may take place. In some of these cases an expert radiation hygiene consultation may be required. This consultation should comprise the expected risks for the unborn while not perturbing the mother or the involved medical staff.

For the risk assessment in case of an in-utero x-ray exposition deterministic damages with a defined threshold dose are distinguished from stochastic damages without a definable threshold dose. The occurrence of deterministic damages depends on the dose and the developmental stage of the unborn at the time of radiation.

To calculate the risks of an in-utero radiation exposure a three-stage concept is commonly applied. Depending on the amount of radiation, the radiation dose is either estimated, roughly calculated using standard tables or, in critical cases, accurately calculated based on the individual event. The complexity of the calculation thereby increases from stage to stage. An estimation based on stage one is easily feasible whereas calculations based on stages two and especially three are more complex and often necessitate execution by specialists.

This article demonstrates in detail the risks for the unborn child pertaining to its developmental phase and explains the three-stage concept as an evaluation scheme. It should be noted, that all risk estimations are subject to considerable uncertainties.

• Radiation exposure of the unborn child can result in both deterministic as well as stochastic damage und hitherto should be avoided or reduced to a minimum.

• In case of radiation a suitable hygiene consultation may be necessary.

• For risk assessment a three-stage concept is applied, which, depending on the radiation exposure, estimates or calculates the dose for the unborn child.

• The radiologist plays a crucial role as a competent advisor and provider of reliable expert information.

Citation Format:

• Scharwächter C, Röser A, Schwartz CA et al. Prenatal Radiation Exposure: Dose Calculation. Fortschr Röntgenstr 2015; 187: 338 – 346

Zusammenfassung

Embryo und Fetus bedürfen eines besonderen Schutzes. In diesem Kontext ist die Notwendigkeit einer Röntgenuntersuchung besonders kritisch zu prüfen. Bei einer nicht vermeidbaren Mitbestrahlung des Unterbauches und damit des Uterus, sollte die Untersuchung bis zum Ende der Schwangerschaft verschoben oder die Möglichkeit alternativer Verfahren erwogen werden. Unter speziellen Umständen kann es jedoch, entweder inzidentell oder nach reiflicher Risikoabwägung gezielt, zu einer Röntgenuntersuchung und konsekutiv zu einer Strahlenbelastung des Ungeborenen kommen. In diesem Fall kann eine strahlenhygienische Beratung erforderlich werden. Diese enthält die zu erwartenden Risiken für das Ungeborene, ohne unnötige Ängste und Sorgen sowohl bei der Schwangeren, als auch bei behandelnden Kollegen zu induzieren.

Für die Risikobewertung werden im Falle einer Exposition in utero deterministische Strahlenschäden mit einer definierbaren Schwellendosis und stochastische ohne Schwellendosis differenziert. Das Auftreten von deterministischen Schäden ist zusätzlich zur Dosis vom Entwicklungsstadium des Ungeborenen zum Zeitpunkt der Strahlenexposition abhängig.

Als Bewertungsschema hat sich im Falle einer Strahlenexposition in utero ein dreistufiges Konzept bewährt. In Abhängigkeit der Expositionsausprägung wird entweder eine Abschätzung der Dosis bzw. eine grobe Berechnung anhand von Rechenmodellen vorgenommen oder es erfolgt im ausgeprägtesten Fall eine auf den Einzelfall bezogene Berechnung so exakt wie möglich. Die Komplexität der Bestimmung nimmt dabei mit jeder einzelnen Stufe zu. Während eine Abschätzung nach Stufe eins normalerweise problemlos machbar ist, ist eine Berechnung nach Stufe zwei und insbesondere drei komplex und oft nur von Spezialisten durchführbar.

Im folgenden Artikel werden die Risiken für das Ungeborene in Abhängigkeit von den verschiedenen Entwicklungsphasen differenziert dargestellt und das Drei-Stufen-Konzept als Bewertungsschema näher erläutert. Hierbei ist zu berücksichtigen, dass die entsprechenden Risikoschätzungen mit nicht unerheblichen Unsicherheiten behaftet sind.

Key words

health policy and practice - radiation effects - radiation safety - pregnancy

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