Patient Dose in Single Radiodiagnostic Examinations in Cantabria (Spain) over a 10-year Period

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1 Patient Dose in Single Radiodiagnostic Examinations in Cantabria (Spain) over a 10-year Period M. Alonso 1, M.J. Castañeda 1, N. Díaz-Caneja 2, I. Gutiérrez 2, G. López 2 1 Servicio de Radiofísica y Protección Radiológica, Hospital Universitario Marqués de Valdecilla, Avda. de Valdecilla 25, E-39008, Santander, Spain M. Alonso: praadm@humv.es ; M.J. Castañeda: pracaj@humv.es 2 Dpto. Física Médica, Facultad de Medicina, Universidad de Cantabria, Avda. Cardenal Herrera Oria s/n, E-39011, Santander, Spain N. Díaz-Caneja: diazn@unican.es; I. Gutiérrez: gutiermi@unican.es Abstract. Implementing a quality assurance program in a radiodiagnostic department and the optimization criteria for this involves determining the dose received by the patient. In 1993, the Radiation Protection Service at Marqués de Valdecilla University Hospital (Santander) began periodic determination of doses received by patients. The regional hospitals in, Sierrallana and began measurement of patient doses in The study analyzes the evolution of values for patient entrance surface dose () and for the dose-area product () in single radiodiagnostic examinations at Valdecilla Hospital over the period The examinations and projections studied are abdomen AP, lumbar spine AP and LAT, pelvis AP, chest PA and LAT and mammography. Mean values for the doses delivered at the four hospitals are compared for the period The values, while showing variation for different years, were generally below the reference values established in the legislation. However, the values are above the proposed reference values. The difference in behaviour between the and values was due to inadequate collimation. The and values for the regional hospitals were generally higher than those for Valdecilla Hospital. The mammography doses at these hospitals were always lower than the reference values. 1. Introduction Implementation of a quality assurance program in a radiodiagnostic department and the optimization criteria necessary for this involves determining the doses received by the patient in the unit. In accordance with European Union guidelines, 1993 saw the start of periodic measurement of doses received by patients at several hospitals belonging to the Health Service of the Autonomous Community of Cantabria (Spain). In 1995, Spanish legislation (Real Decreto 2071/1995) [1] made it compulsory to verify these doses (providing reference values for patient entrance surface dose in single examinations) and to specify the technical conditions in which the examination is performed. These requirements were maintained in the new regulations published in 1999 (Real Decreto 1976/1999) [2]. 2. Material and Methods This study was carried out on data obtained on doses delivered to patients at the University Hospital Marqués de Valdecilla in Santander, and at the regional hospitals of, Torrelevega and, which together represent a total 1,675 beds and attend a population of 545,275 inhabitants. The total number of examinations analyzed is 10,269. In order to study the possible influence of the implementation of a quality assurance program, an analysis was made of the evolution in doses over the period at Valdecilla Hospital and the values for the doses delivered at the four hospitals of the Cantabrian Health Service were compared for the period Average dose values were also compared with the reference values for those explorations for which such values have been established in the legislation. Values for the patient entrance surface dose () and the dose-area product () were used for the following single examinations: abdomen AP, lumbar spine AP, lumbar spine LAT, pelvis AP, chest PA, chest LAT and mammography. 1

2 The data obtained for each examination were as follows: values selected for tube kilovoltage, current, exposure time and charge, field size at the patient entrance surface, film size, source-patient distance and source-film distance. The area index (AI) was calculated as the ratio between the area of the radiation field at the patient entrance surface and the area of the film backprojected onto the patient entrance surface. The dosimetry variables studied were the and the. The study was performed on real patients and the average values were calculated in two ways, per room and per examination (grouping all rooms together). Excluded from the study were patients under 14 years of age and those rooms with fewer than 7 patients. The values for the dosimetry variables were obtained either from measurements made with a PTW Diamentor transmission chamber installed at the collimator exit, or from the tube output determined at the corresponding quality control performed on the equipment. Basically, the first method was used for general radiography equipment at Valdecilla Hospital, and the second for the mammographic units and for the general radiography rooms in the regional hospitals. All measurements and data collection were carried out by technicians of the Radiation Protection Service at Valdecilla Hospital. The was determined from the taking into account the backscatter factor, F rd (1.35 for conventional examinations and 1.08 for mammography) [3], the correction factor for pressure and temperature, F pt (1.0 at sea level), the ratio between mass attenuation coefficients in tissue and in air, F ta (1.06 for conventional x-rays and 1.00 for mammography, since this exploration is performed in air), and the area of the radiation field at the patient entrance surface, S, according to the following equation: = F rd F pt F ta S The measurement system used was calibrated at the Calibration Laboratory of National Dosimetry Centre. 3. Results and Discussion Table I gives the average values weighted in terms of the number of examinations per room for the, and AI for the above-mentioned single examinations, except mammography, at Valdecilla Hospital over the period The average values for each examination overall are lower than the weighted average values per room. The results presented in this paper correspond to the study per room, since they give a better indication of the influence of the application of the quality assurance program than those of the study per examination. The showed a marked decrease in the first few years after implementation of the quality assurance program, with an increase for some examinations (lumbar spine AP and chest PA and LAT) after the year This behaviour is similar to that of the and for the same examinations, although the decrease in the first few years was less pronounced, except for abdomen AP. The increase after the year 2000 was also smaller. The variation in AI was similar for all examinations except abdomen AP and lumbar spine AP; in the latter case the AI remained practically constant around the value 1. Although the values for Valdecilla Hospital varied over the years, they were generally below the reference values established in the legislation. In contrast, the values, the variable showing the greatest relation with radiological risk to the patient, were much higher than the proposed reference values during the first years of the study [4], but in recent years, these values have been brought close to, or even lower than, this level, except for chest LAT. This different behaviour in the and values is due to inadequate collimation. This was assessed by determining the AI, that should be unity or lower, but in some examinations it was higher than 2. 2

3 Table I. Average values weighted in terms of the number of examinations per room for the variables, and AI, and the number of rooms and the total number of examinations studied per year at Valdecilla Hospital. Abdomen AP Lumbar spine AP Lumbar spine LAT Pelvis AP Chest LAT Chest PA AI

4 Table II gives the average values weighted in terms of the number of examinations per room for the, and AI, for the six examination types, at the three regional hospitals for the period The and values for the regional hospitals were generally higher than those for Valdecilla Hospital, except for chest LAT. The AI values are similar to those for Valdecilla Hospital. Table II. Average values weighted in terms of the number of examinations per room for the variables, and AI, and the number of rooms and the total number of examinations studied per year at the three regional hospitals. Abdomen AP Lumbar spine AP Lumbar spine LAT Pelvis AP Chest LAT Chest PA Hospital AI The values for mammography at Valdecilla Hospital and at the regional hospitals for the whole of the period are shown in Table III. There was a considerable decrease for the regional hospitals, with values for the last two years remaining below the reference level. For the years 2000 to 2002, the values for Valdecilla Hospital were clearly above the reference level because of changes made to the screen-film system. After the pertinent corrections had been made, values were again close to the reference values. 4

5 Table III. Average values weighted in terms of the number of examinations per room for the, and the number of rooms and the total number of examinations studied per year at the hospitals named. Mammography 10 Hospital Valdecilla Conclusions The application of a quality assurance program has led to a significant reduction in the dose delivered to patients, although changes made to the imaging system have caused temporary increases in doses. The influence of the operator on the dose delivered to the patient is important, and in addition to controlling the equipment, it is also essential to provide the necessary training for these technicians. s 1. Real Decreto 2071/1995, de 22 de diciembre, por el que se establecen los criterios de calidad en radiodiagnóstico. BOE de 23 enero Real Decreto 1976/1999, de 23 de diciembre, por el que se establecen los criterios de calidad en radiodiagnóstico. BOE de 29 diciembre European Commission. European guidelines on quality criteria for diagnostic radiographic images. EUR EN. Ed. By Carmichel J.H.E., Maccia C., Moores B.M., Oestmann J.W., Schibilla H., Teunen D., Van Tiggelen R. and Wall B.F. Brussels (1996). 4. Díaz-Caneja N., Alonso M., Arranz L., et al. (Grupo Aula Salinas) Propuesta de un valor de referencia del producto dosis-área en exploraciones simples de radiodiagnóstico en España. Communication presented at the XII National Congress of the SEFM (Spanish Society of Medical Physics). Santander, Spain, September