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ANALYSIS OF THE PATIENT EXPOSURE TO RADIATION FROM MEDICAL DIAGNOSIS : EXPOSURE DATA AND QUALITY ASSURANCE

Objective

PROJECT 1: ASSESSMENT OF THE SOMATIC DOSE RELATED TO MEDICAL DIAGNOSTIC RADIOLOGY.

THE FINAL OBJECTIVES OF THE RESEARCH PROPOSED, ARE TO COMPLETE PREVIOUS INVESTIGATIONS ON ABSORBED DOSES DUE TO DIAGNOSTIC X-RAY EXAMINATIONS, IN ORDER TO ESTIMATE THE COLLECTIVE RISK ASSOCIATED TO THE USE OF IONIZING RADIATION IN MEDICINE.

PROJECT 2: QUALITY ASSURANCE IN MEDICAL DIAGNOSTIC RADIOLOGY
THE MAIN OBJECTIVES OF THIS PROJECT ARE THE FOLLOWING.
The objectives of the project are to complete previous evaluations of the absorbed dose due to diagnostic radiology procedures in France carried out within the framework of the 1982 to 1985 Commission of European Countries (CEC) radiation protection programme in order to estimate the collective risk associated with the use of ionising radiation in medicine (conventional diagnostic examinations).

As far as the genetically significant dose (GSD) is concerned, the figure obtained from the survey represents approximately 14% of the total GSD from natural background. Concerning the International Commission on Radiological Protection (ICRP) remainder organs their contribution to the effective dose equivalent associated with each examination category must be stressed. In particular, in almost 60% of the examinations considered, doses received by these organs represent more than 40% of the effective dose equivalent.
Over 80% of the routine examinationsyearly carried out in France have effective dose equivalents that are more than the average per caput annual doseof 2 mSv due to the natural background radiation in France. Estimate of the collective effective dose equivalent associated to the radiological practice is 86,000 person sievert ie an individual effective dose equivalent of 1.58 mSv per year (1.48 for females and 1.70 for males). Finally, there have been few comprehensive publications of organ dose data for diagnostic radiological procedures, which probably reflect the difficulties of achieving suitable dose estimates for many organs. Comparison of our organ dose data with results from similar surveys indeed indicates large discrepancies for certain organs and examinations, which must be due at least in part to the differences in dosimetric technique used. Although higher levels of patient exposure have been found for France (the British collective dose per E6 inhabitants is 6 time lower that the French collective dose), without comparison of the image quality a s well as the patient doses, it is difficult to verify whether optimal conditions have been applied in other countries. The introduction of quality assurance programmes in diagnostic radiology, which is being encouraged in Europe by the CEC, might certainly help to establish and maintain optimal procedures in this field.

The newborn pelvic X-rays:
The total number of pelvis X-ray examination performed on 0 to 1 year old children for diagnosing of the congenital hip dysplasia (CHD) was estimated. A figure of 725,400 pelvic X-rays was found which represents a rather high number of examinations per 1000 inhabitants: 1563 and 550 examinations for 1000 girls and boys respectively.
Out of these data, only the examinations which were declared by the radiologists as routinely performed were selected. The figures concerning this subpopulation showed that, 1 out of 3 boys and 2 out of 3 girls undergo, in the first year of their life, a pelvic X-ray, indicating a quasisystematisation of this radiological practice although no official systematic CHD X-ray diagnosis programme exists. As far as the children/s age distribution is concerned almost 22.5% of these examinations are carried out in the first 10 days of life, slightly more than 40% between the third and fourth month and 37.5% after the fourth month. Knowing that before the third month of life the pelvic X-ray is not reliable method for CHD diagnosis, the routine X-ray done in the first few days may thus appear as needlessly expensive and irradiant.
Concerning the dose evaluation problem, measurements have been performed directly on 35 children aged between 3 and 5 months (16 girls and 19 boys) by using thermoluminescent dosimeters (TLD) (lithium borate chips). In the case of male children, gonads were shielded, while for girls no special protection was set up. Only additional diaphragms were used to reduce the radiation field (diameter of 10 cm). All studied examinations were carried out on Titanos 50 tables suitable for radiopaediatry and with a 3-phased generator.
The skin dose in the beam centre was estimated: as far as the gonad dose in concerned, TLDs were on the same level with the iliac joints over the presumed location of the ovaries for girls, and on the scrotum for boys. The figures obtained were: 0.01 mGy for testes and 0. 30 mGy for the ovaries.
If a systematic X-ray diagnosis programme existed in France the resulting genetic risk could then be evaluated. According to the International Commission on Radiological Protection (ICRP) recommandations the risk of serious hereditary ill health within the 2 first generations following the irradiation of either parents is about E-2 Sv{-1}. Both parents being involved in a radiological mass screening and assuming there is no gonadal shielding in females, the genetic risk would be 1.02/695,000 ie 1.45 for 1 million births.

Quality assurance in mammography:
Breast cancer remains the major cause of disability and death among women. The most relevant way to reduce this incidence relies upon the early detection of infraclinical lesions such as tiny microcalcifications or low contrast lesions which may be currently considered as indications of malignancy. It is also widely recognised that mammography is the most effective diagnostic imaging technique to be performed in order to detect such minute details and irregular borders of lesions.
In the last 2 decades many countries have carried out breast cancer screening programme on asymptomatic women by exclusively using this technique.
Nevertheless, many controversies have arisen in the form of scientific debates over both radiographic techniques to be used (type of detector, number of projections) and epidemiological considerations (age of patients to be screened, dose risk relationship curve). All the local and national trials forthcoming are characterised by the absence of well defined quality control procedures. It is important to proceed towards a general overview of a sample of the radiological equipment which potentially could be used within the framework of such trials. In doing so, a pilot survey of 75 dedicated mammographic units installed in both public hospitals and private radiological offices all over in France was conducted and radiological techniques likely to influence both breas t dose and image quality, were evaluated.

A first general comment about the results deals with the necessity of harmonising the various parameters which can interact with both dose and image quality. This might be achieved by introducing quality control procedures. Indeed, checking the beam quality seems the first action to be undertaken in order to ascertain for instance the reliability of kilovoltage.
Furthermore, estimates of optical densities associated with routine operating conditions suggest that the calibration of phototimer should be suited to the kilovoltage actually used as a function of the receptor sensitivity. In the same way, skin entrance dose values might be lowered by using exposure times shorter than 1 second. On the contrary, in spite of the increase in entrance skin dose, antiscatter grids significantly improve the image quality and their use should be promoted on a larger scale.
Despite the small number of X-ray units considered in this pilot survey and the experimental character of this study, all these considerations, together with clinical aspects (eg examination techniques towards the variation of the breast density), call for a need for setting up a quality assurance programme in mammography in France. Besides quality control, such a programme might obviously include many activities like preventive maintenance, equipment calibration, training and in service education of technologists and spreading of information. Only under such conditions, and particularly in the context of a breast mass screening project, the quality of mammograms would be guaranteed with a consequential real benefit for patients in terms of reliability of diagnosis and dose reduction.

The objectives of the project are as follows:
to provide practitioners with a provisional acceptable list of radiological criteria, technical criteria and dosimetric criteria which could be useful to judge the quality of the radiographs routinely undertaken in diagnostic radiology;
toassess the relevance of these criteria for 6 types of X-ray examination commonly carried out in everyday radiological practice (chest, skull, lumbar spine, pelvis and sacrum, urinary tract and breast);
to providepractical considerations on how to reduce and to optimise patient doses in diagnostic radiology.

In view of proceeding toward the harmonisation and optimisation of radiological techniques commonly used in different European countries, the relevance of quality criteria for radiographic images together with dose requirements were checked on about 900 examined patients. Due to the type of X-ray projections considered, more than 1200 questionnaires concerning the X-ray films were collected and evaluated through a scoring system. This approach has provided information on suitable technique (automatic exposure control (AEC) system and fast speeds) for reducing and optimising patient dose while keeping the essential medical information imaged on the film. Furthermore, this analysis puts forward 2 main domains which should be further taken into consideration:
personnel training in radiation protection (radiologists and radiographers);
establishment of quality assurance programmes in diagnostic radiology (good usage of radiological equipment and reduction of wasted films).

Through this approach, which is easily applied in an X-ray department, a possible modification of the current radiological practices might be envisaged without any interference with the final result of the examination, the diagnosis
Finally, this first step toward the optimisation of the patient radiation protection, emphasises, once more, the necessity to stimulate an active collaboration between radiologi sts and medical physicists.

The total number of computerised tomography (CT) examinations performed yearly has rapidly increased given the number of new CT machines installed each year. Within this context, it seemed to assess the effective dose equivalent associated with such a radiological technique as well as its impact on the patient collective dose.
As a first tentative attempt, a survey was conducted to establish a statistical data base concerning 15 CT scanners operating in the Provence Alpes Cote d'Azur region of France. CT technical related data (kilovoltage, tube current, filtration), patient related data (age, sex, anatomical region examined) and examination related data (slice number, slice thickness, exposure time) were collected for about 700 different CT examinations. To allow for variations in X-ray output, beam collimation and scanning geometry between all considered CT scanners and between different selections of the scanning parameters on a particular machine, the free in air axial dose profiles for a single slice at the centre of rotation were measured for each commonly used set of scanning parameters on each scanner. For such a purpose, a row of thermoluminescent (TDL) was used, with individually known sensitivities, spaced at approximately 1 mm intervals and of sufficient number to cover at least twice the nominal slice thickness and aligned along the axis of rotation.
Results of these dose measurements were matched with data collected during the survey, and used to assess, through a Monte-Carlo simulation program provided by the National Radiological Protection Board (NRPB) for the specific CT machines considered, the dose contribution of each scan slice to the dose received by each organ as a function of the anatomical region examined. Effective dose equivalents for all examinations were therefore evaluated by applying the International Commission on Radiological Protection (ICRP) weighting factors.

The free in air axial dose profiles measured at the centre of rota tion were normalised to the nominal slice thickness to obtain the CT Dose Index (CTDI) for each single slice. Considerable CTDI variations were observed in the survey depending on the slice thickness and on the CT machine studied. Besides such variations in dose, large discrepancies were found concerning the technical protocols (number of slices) followed in performing different type of CT examinations as a function of the part of the body examined: 11 to 13 slices, on average, during an head scan and 22 to 24 slices, on average, during an abdomen examination.

Average organ doses of each CT examination type observed in the survey and the corresponding effective dose equivalent values were measured. Average effective dose equivalent (EDE) values range markedly depending of the examination type (factor of 6 between skull and thorax CT scan for instance). Furthermore, maximum EDE values may occur when particular examination techniques are used (high resolution mode, greater than 30 slices). This is particularly true for abdomen and thorax for which maximum EDE is about 30 mSv and the mean EDE is about 10 mSv.
Taking into account the relative frequency of each examination type estimated through the national survey, the collective effective dose equivalent associated with the CT practices was assessed combining statistical and technical data gathered. A figure of 6318 person-Sv was found corresponding to 1,300,000 CT examinations performed in 1987, ie about 7% of the total collective effective dose equivalent attributable to diagnostic radiology practices.
PROJECT 1: A. "REMAINDER" DOSES ASSESSMENTS (OTHER ORGANS IN THE SENS OF ICRP PUBLICATIONS 26)
B. ASSESSMENT OF THE CONTRIBUTION OF COMPUTED TOMOGRAPHY TO THE COLLECTIVE DOSE FROM DIAGNOSTIC RADIOLOGY

PROJECT 2:
THE MAIN OBJECTIVES OF THIS PROJECT ARE THE FOLLOWING:
A. THE EVALUATION OF THE RELATIONSHIPS EXISTING BETWEEN THE IMAGE DETECTOR QUALITY, THE INTERPRETATION EQUIPMENT QUALITY AND THE DOSE RECEIVED BY THE PATIENTS.
B. FEASIBILITY ANALYSIS OF DOSE REDUCTION THROUGH EXAMINATION PROTOCOLS
C. QUALITY ASSURANCE IN PAEDIATRIC RADIOLOGY: INDICATIONS OF PELVIS EXAMINATION IN THE DIAGNOSIS OF HIP DYSPLASIA
D.THE IMPACT OF INNOVATION ON DOSE REDUCTION: THE CASE OF DIGITAL ANGIOGRAPHY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CAATS
Address

92263 Fontenay-aux-roses
France