Calculation of the maximum allowed ambient dose rate outside CT rooms to quantitatively assess the structural shielding performance.

The goal of this study was to develop a method to quantitatively assess the structural shielding performance of computed tomography (CT) rooms in Switzerland. The method was based on the comparison between calculated maximum allowed ambient dose rate (DR) and measured ambient DR in adjacent spaces. If the measured DR exceeds the calculated maximum allowed value, additional shielding is required; otherwise the shielding is sufficient. The maximum allowed ambient DR was calculated using two different shielding concepts either based on the tube loading of the scanner or on the accumulated dose length product of the scans. The method was validated for 36 spiral CT head protocols. The average ratio of the maximum allowed ambient DR between both concepts was 1.11 (range 0.57-2.14). Among 36 CT rooms, 7 room boundaries were insufficiently shielded. In conclusion, this method allows the authority to check on-site the compliance of the structural shielding with legal requirements.

An audit of diagnostic reference levels in interventional cardiology and radiology: are there differences between academic and non-academic centres?

A wide variation in patient exposure has been observed in interventional radiology and cardiology. The purpose of this study was to investigate the patient dose from fluoroscopy-guided procedures performed in non-academic centres when compared with academic centres. Four procedures (coronary angiography, percutaneous coronary intervention, angiography of the lower limbs and percutaneous transluminal angioplasty of the lower limbs) were evaluated. Data on the dose-area product, fluoroscopy time and number of images for 1000 procedures were obtained from 23 non-academic centres and compared with data from 5 academic centres. No differences were found for cardiology procedures performed in non-academic centres versus academic ones. However, significantly lower doses were delivered to patients for procedures of the lower limbs when they were performed in non-academic centres. This may be due to more complex procedures performed in the academic centres. Comparison between the centres showed a great variation in the patient dose for these lower limb procedures.

Patient doses in CT examinations in Switzerland: implementation of national diagnostic reference levels.

Diagnostic reference levels (DRLs) were established for 21 indication-based CT examinations for adults in Switzerland. One hundred and seventy-nine of 225 computed tomography (CT) scanners operated in hospitals and private radiology institutes were audited on-site and patient doses were collected. For each CT scanner, a correction factor was calculated expressing the deviation of the measured weighted computed tomography dose index (CTDI) to the nominal weighted CTDI as displayed on the workstation. Patient doses were corrected by this factor providing a realistic basis for establishing national DRLs. Results showed large variations in doses between different radiology departments in Switzerland, especially for examinations of the petrous bone, pelvis, lower limbs and heart. This indicates that the concept of DRLs has not yet been correctly applied for CT examinations in clinical routine. A close collaboration of all stakeholders is mandatory to assure an effective radiation protection of patients. On-site audits will be intensified to further establish the concept of DRLs in Switzerland.

Diagnostic and interventional radiology: a strategy to introduce reference dose level taking into account the national practice.

The purpose of this study is to present a strategy to define the reference dose levels for fluoroscopic, dose-intensive examinations. This work is a part of the project of the Federal Office of Public Health of Switzerland to translate the guidelines of the International Commission on Radiological Protection and the European Union into action. The study will also be used to set reference dose levels on the basis of a national survey. All the fluoroscopic units, involved in the survey, were equipped with a KAP (kerma-area product) meter. All KAP meters were first calibrated to ensure the comparability of the dose measurements. The doses and the dose rates together with subjective image quality measurements were acquired in all the centres. Eight types of examination were chosen by a panel of radiologists, and each of the five centres involved agreed to monitor 20 patients per examination type. A wide variation in the dose and the image quality in fixed geometry was observed. For example, the skin dose rate for abdominal examinations varied in the range of 12-42 mGy min(-1) for comparable image quality. Average KAP values of 67, 178, 106, 102, 473, 205, 307 and 316 Gy cm2 were recorded for barium meal, abdominal angiography, cerebral angiography, barium enema, hepatic embolisation, biliary drainage, cerebral embolisation and femoral stenting, respectively. The values obtained in this limited study are generally higher than the ones available in the literature and strategies to optimise these studies have to be discussed. A strict control concerning the denomination of the examination type involved in such a study is mandatory to obtain reliable data. This can only be done through a close collaboration between physicians, radiographers and medical physicists.