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THE EFFECTIVE DOSE EQUIVALENT DUE TO X-RAY DIAGNOSTIC EXAMINATIONS AND THE IMPACT OF QUALITY CONTROL ON MEDICAL EXPOSURE

Objective

The aim of this work is to assess the relationship between the radiation exposure of interventional radiology and the risk of alternative methods, and to investigate the storage phosphor mammography with a view to reducing the exposure.
The 2 major advances in radiology are digital imaging systems and interventional radiology (IR). A general survey has been carried out in order to evaluate the exposure associated with these techniques. Evaluation of the initial results for patient exposure show angioplasty to be the most frequently applied procedure. Patient exposure involves only the type of the x-ray unit and the sensitivity of the imaging system, but also the time of flouroscopy and the number of images per examination. A large number of such data is necessary to calculate an average of radiation induced cancer risk. The lethal risk of the patient caused by the sickness without therapy is 1 E-1, caused by surgery 1 E-2 and caused by radiation perhaps 1 E-4 for IR.

The dose equivalent was measured for staff in IR and Angiography giving the following results:
the exposure of the hands with IR was lower than that with angiographies;
the mean value of the dose equivalent to the hand was 0.25 mSv per examination; an excess of the dose limit of 500 mSv per annum was normally not to be expected;
considering the variation of the individual doses, correlations between exposures and parameters cannot be proved;
undercouch tubes substantially reduced the exposure of the examiner's hands;
the individual examination technique was an important factor of exposure;
an individual finger dosimetry was recommended to each examiner;
additional protection from radiation was recommended.

The digital storage phosphor foils offer a new imaging with the possibility of reducing the patient exposure in medical diagnostic radiology. It must also be examined whether it is suitable for the mammography. A comparison was made to evaluate the quality of the image of storage phosphor foils and the conventional mammography film screen combination by finding out physical parameters and by analysing receiver operating characteristic (ROC). The advantages of the digital radioscopy (DLR) are found in the bigger object l atitude giving a general good image impression. The subcutane regions and the envolvement of the skin can be judged much better. The individually elaborated image is subjectively better. The image shows a good blackening irrespective of the exposure.
Opposed to these, there are disadvantages of the DLR. The recognition of microcalcereous deposits is less clear in the digital image. A black halo appears around bigger calcifications which seems very unnatural. Brightenings in the honeycomb structured graphs of fatty tissue do slightly disturb the image impression. Underexposed images have a clearly intensified noise.
The study shows already, that a reduction of the exposure in the digital image dose obviously entail inferior image quality. This means that with the storage phosphor mammography a reduction of the exposure cannot be realized at the present time.
A central documentation of interventional radiology was started. More than 100 hospitals and medical surgical interventions have been included. All kinds of interventional techniques were taken into account with this questionnaire. In addition to radiation exposure parameters, like time of fluoroscopy and number and kind of images, exemplary dose measurements have to be considered. The standard data of the angiographic unit will also be gathered. The mean values of the measured and calculated organ and effective dose equivalents and total absorbed energy enable a comparison of the risk of cancer induced by radiation with the risk of operation and narcosis. A great collective is necessary to get representative results, considering the strong variation of dose values.

A further clinical study of angiography and interventional radiology has started to determine the exposure of staff. At both conventional and digital overtable and undertable X-ray tube units the dose at the fingers will be measured by official ring-dosemeters. Additional TLDs will be used to determine the dose to head and neck.

The third part is to investigate the suitability of storage phosphor radiography for mammography. Objective physical parameters like spatial resolution, signal-to-noise ratio or Wiener Spectrum will be correlated with the dose at the imaging system. In addition a ROC-Analysis (Receiver Operating Characteristic Curve) compares digital and conventional mammograms.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Friedrich-Alexander-Universität Erlangen Nürnberg
Address
Krankenhausstraße 12
91054 Erlangen
Germany