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DOSE ASSESSMENT AND QUALITY ASSURANCE IN DIAGNOSTIC RADIOLOGY

Objective

IN PORTUGAL THE FREQUENCY OF RADIOLOGICAL EXAMINATIONS IS ESTIMATED TO BE IN THE SAME ORDER OF MAGNITUDE AS IN OTHER CEC COUNTRIES. IT IS GENERALLY ACCEPTED THAT THERE IS AN OVERUSE OF X-RAY EXAMINATIONS TAKING INTO ACCOUNT THE LEVEL OF HEALTH CARE IN THE COUNTRY. ON THE OTHER HAND THERE ARE SOME DEFICIENCIES IN CERTAIN COMMON RADIOLOGICAL PRACTICES AND TO A CERTAIN EXTEND OBSOLETE EQUIPMENT IS STILL EMPLOYED. THE PATIENT DOSES TO THE PORTUGUESE POPULATION WILL BE ASSESSED IN ORDER TO EVALUATE RADIOLOGICAL PRACTICES AND TO STUDY POSSIBLE IMPROVEMENT BY INTRODUCING QUALITY ASSURANCE MEASURES WITH A VIEW TO REDUCING UNNECESSARY DOSES TO PATIENTS.
A survey of Portuguese mammographic centres during 1988 and 1989 revealed that the equipment had up to date technical specifications with 90% of X-ray equipment dedicated, 96% had molybdenum anodes and 50% used moving grids. Image quality was evaluated for a simulated craniocaudal projection. The median glandular dose per image was estimated at 1.1 mGy, 0.8 mGy for dedicated units without grids, 1.0 mGy for stationary grids and 2.0 mGy for moving grids. Entrance surface dose per image was (mean) 6.0 mGy. The annual frequency of mammographies was 16.5 per 1000 inhabitants and 3.4 mammographies per 100 X-rays. A quality control programme was found to contribute significantly to the optimization of mammographic systems and the availability of a dedicated film processor was found to be a crucial element in the improvement of results.

A national survey was carried out in intraoral dental radiography (1989 to 1990). Film processing was manual in 69.1% of premises and in 56% there was no control of development time or temperature. The mean value for entrance dose for a molar tooth radiography was calculated to be 9.2 mGy.

A survey of computer tomography (CT) installations was carried out in 1990. Data were collected from 36 scanners. Maintenance and quality control were assured by manufacturers in 97% of the installations. Image quality evaluations gave good agreement with adopted values. Peak dose per head examined gave a median value of 50.6 mGy (surface) and 42 mGy (centre). Mean doses free in air were higher than published values in other European Economic Community (EEC) countries.

The methodology applied to population dose assessment was based on the Nationwide Evaluation of X-ray Trends (NEXT) programme. When compared to recommended EEC values of average voltage, chest projection used lower than recommended values, the skull projection voltage value was within the lower limit and the abdomen projection did not have an EEC reference. The lumbosacral spine vo ltage was within EEC range. Skin entrance exposures were compared with an Italian study and were found to be lower than the latter.
RESEARCH WILL BE CARRIED OUT ALONG THE FOLLOWING STEPS:

POPULATION DOSES ASSESSMENT
- EVALUATION OF THE FREQUENCY OF ALL TYPES OF RADIOLOGICAL EXAMINATIONS USING THE AVAILABLE DATA FROM HEALTH STATISTICS.
- SELECTION OF THE MOST SIGNIFICANT EXAMINATIONS TAKING INTO ACCOUNT THEIR FREQUENCY AND ASSOCIATED DOSES.
- DOSE MEASUREMENTS SHALL BE TAKEN IN SIX SELECTED HOSPITALS CONSIDERING THEIR RANKING IN THE NATIONAL HEALTH SERVICE AND RADIOLOGICAL EQUIPMENT STATUS.
- PROCESSING AND ANALYSIS OF THE DOSE DATA WILL UTILISE METHODS AND MODELS DEVELOPED IN SIMILAR STUDIES ALREADY CARRIED OUT IN OTHER MEMBER STATES.

QUALITY ASSURANCE
- INVENTORY OF MAMMOGRAPHIC AND CT EQUIPMENTS AND CORRESPONDING PRACTICES TO GET INFORMATION ON THE MOST IMPORTANT TECHNICAL PARAMETERS AFFECTING DOSES AND IMAGE QUALITY: THE WORK WILL BE CARRIED OUT FOLLOWING THE PROTOCOLS ESTABLISHED FOR SIMILAR ACTIONS IN OTHER MEMBER STATES.
- DEVELOPMENT OF QUALITY ASSURANCE PROGRAMMES FOR DENTAL MAMMOGRAPHY AND CT INSTALLATIONS, AND APPLICATION OF THESE PROGRAMMES IN SOME RADIOLOGY DEPARTMENTS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

LABORATORIO NACIONAL DE ENGENHARIA E TECNOLOGIA INDUSTRIAL
Address
Dpsr Azinnhaga Dos Lameiros Estrada Do Paco Do Lumiar 22
1699 Lisboa
Portugal