[en] Vascular radiology includes procedures in which the radiologist or other medical specialist uses the radiological image to diagnose or treat a specific vascular structure. In the published MIRA-2004 report (Milieu- en natuurrapport Vlaanderen) is mentioned that in 2001 the diagnostic vascular procedures comprised only 0.9% and the interventional (cardiology) procedures only 0.4% from the total number of performed radiological medical examinations in Flanders. Notwithstanding the frequency is low, their contribution to radiation exposure in medicine is considerably higher in respect to all X-ray examinations. Due to the complexity of these procedures, the application of the ALARA-principle, keeping doses as low as reasonably achievable without jeopardizing image quality, is a great challenge. It is obvious that optimization of patient doses necessitates a reliable insight in dose levels associated with the different examinations. However, in Belgium there is a great lack of quantitative data in vascular radiology and no explicit instructions are available on how the work could be done practically. Therefore, the first purpose of the study was to define, to measure and to calculate doses to patients in 7 different hospitals. In the thesis, patient doses are measured and calculated for 3 specific vascular procedures: angiography of the lower limbs, angiography of the carotid arteries and cerebral embolisation. The doses are evaluated against different technical parameters of the equipment and of the working procedure. In view of optimization purposes, a protocol for performing dose audits in vascular radiology is suggested. From the results and conclusions in this study, some practical guidelines could be given for the radiological protection of the patient. For 158 patients, relevant parameters as tube voltage (kVp), tube load (mAs), field size, number of frames, fluoroscopy times etc. were recorded. With a flat ionization chamber, positioned in the radiation beam, the product dosexfield area (DAP) was measured for every beam projection separately. Skin doses were measured with thermoluminiscent dosimeters (TLDs) attached to the skin of the patient. These measurements confirmed that radiation doses are high and that for every procedure a large dose variability exists between the different hospitals and between the patients within one hospital. The quantification and analysis of patient doses for procedures of this kind was not easy, as the procedures are complex and not performed frequently. The study also learned us that 'effective dose' is a useful quantity to estimate in view of dose optimization. The effective dose is the weighted sum of organ doses and therefore can not be measured directly. By means of the Monte Carlo computer code, new and appropriate conversion coefficients were determined for the calculation of effective dose for vascular radiology procedures. If every beam projection in the procedure is considered separately, the calculation of effective dose is very complex and only suitable for studies with a small amount of patients involved. For that reason, also a practical method to calculate the effective dose was worked out, for which only one conversion coefficient is used in combination with the total DAP-value of the procedure. Different national and international organizations have recommended the use of patient dose audits in diagnostic radiology as a means of inter institutional comparison and the establishment of reference dose levels. Several studies 2,3,4 indicated that the performance of dose audits could reduce the difference between the highest and lowest measured dose with a factor of 2. Because of the high doses associated with vascular radiology, dose surveys could here also be of obvious benefit, but will not be straightforward due to the complexity of the procedures. The thorough analysis of the patient doses against all possible technical parameters of the equipment and the work procedure, made it possible to set up a protocol for the performance of dose audits in vascular radiology. We propose to register, in addition to the total DAP-values, also parameters as total number of frames, average kVp en possible copper filtration. These data can be used to set diagnostic reference levels (DRLs) or to compare them with existing DRLs per procedure. The information about the energy spectrum of the radiation (kVp and filtration) also makes it possible to estimate the effective dose. Finally, the extensive dose analysis leads to the proposition of some practical guidelines, in order to restrict patient dose, while maintaining an appropriate image quality. Although the current digital systems for vascular radiology need a lower radiation intensity compared to the conventional film-screen systems, it was found that in practice much more images were taken with the digital systems. If the number of frames is sufficiently reduced and if an appropriate dose level is set at the entrance of the image intensifier, depending on the type and the purpose of the procedure, the dose could already be substantially reduced. Although such guidelines can be raised by medical physicists, it will remain the choice of the radiologist if and how they will be implemented in practice. Keeping the medical staff informed and alert about radiation protection is therefore an important issue in the process of optimization

[en] Monitoring of workers constitutes an integral part of any radiological protection program. However, unresolved issues in radiation protection of medical staff still remain. Research and establishment of guidelines are necessary on a variety of issues such as extremity dosimetry (fingers, eye lenses, etc), the use of double dosimetry above and below lead aprons, or the use of electronic personal dosimeters in interventional procedures. Medical practices are also evolving fast, and new techniques with ionising radiation emerge very regularly, thus implying the need of radiation protection measures for medical staff, and the implementation of new monitoring programs. In some medical applications of radiation there is an increased risk of high local exposures because of direct handling of sources or the use of beta-emitters. However, despite the large number of workers that are exposed in the medical field worldwide, only few measurements of extremity doses have been reported in the literature. Some activities of EURADOS Working Group 9 (WG9) were sponsored by the European Commission in the CONRAD project. This CONRAD project was aiming at the coordination of research on radiation protection at the workplace. Working group 9 has been involved in the coordination and promotion of European research in the field of Radiation Protection Dosimetry for Medical Staff. One of the objectives of this working group was to formulate the state of the art and to identify areas in which improvements were needed. For some of these medical applications the skin of the fingers is the limiting organ from the point of view of individual monitoring of external radiation. The wide variety of radiation field characteristics in a medical environment, and the difficulty of measuring a local dose that is representative for the maximum skin dose (usually with one single detector), makes it difficult to perform extremity dosimetry with an accuracy similar to whole-body dosimetry. Therefore a subgroup of WG9 dealt specifically with the use of extremity dosemeters in medical radiation fields. Active personal dosimeters (APDs) are very efficient tools to monitor occupational doses in real time during exposure and provide selectable alarm levels to avoid high doses. Interventional radiology operators belong to a specific worker category, which would benefit from a real time, accurate assessment of their dose. Another subgroup dealt with the adequate dosimetry of scattered photons, using APDs. They must be able to respond to low-energy (10-100 keV) and pulsed radiation with relatively high instantaneous dose rates

[en] In vascular radiology, the radiologists use the radiological image to diagnose or treat a specific vascular structure. From literature, we know that related doses are high and that large dose variability exists between different hospitals. The application of the optimization principle is therefore necessary and is obliged by the new legislation. So far, very little fieldwork has been performed and no practical instructions are available to do the necessary work. It's indisputable that obtaining quantitative data is of great interest for optimization purposes. In order to gain insight into these doses and the possible measures for dose reduction, we performed a comparative study in 7 hospitals. Patient doses will be measured and calculated for specific procedures in vascular radiology and evaluated against their most influencing parameters. In view of optimization purposes, a protocol for dose audit will be set-up. From the results and conclusions in this study, experimentally based guidelines will be proposed, in order to improve clinical practice in vascular radiology

[en] The effective dose is a quantity that is used to express the risks for stochastic effects. In view of optimization of patient doses, the effective dose can be useful tool. Conversion coefficients (CCs)are used to calculate this effective dose, starting from easily measurable quantities. CCs are widely available, which are calculated for standard phantoms. Because every patient is different, however, inaccuracies will be introduced, using these standard CCs for all patients. This study quantifies the difference in organ doses and effective dose between a standard model and 2 thicker phantoms. The determination of CCs is done for 2 different examinations (Abdomen AP and Thorax PA) with the MCNP computer code. The calculated conversion coefficients are also applied to patient doses (DAP and ESD) that were measured in 3 central and technical parameters as well as patient dimensions were registered. The effective dose for patients larger than the standard phantom (equivalent diameter de=22,9kg/m) is overestimated when calculated with the standard CCs. As well for the abdomen as thorax examination, the overestimation for a patient with de=24,4kg/m is around 18% using DAP and 22% using ESD measurements. For a patient with de=25.8kg/m effective dose is overestimated by nearly 34% using DAP and 39% for ESD measurements. (Author)

[en] The performance of a single or double dosimetry (SD or DD) algorithm on estimating effective dose wearing radioprotective garments (E_RPG) depends on the specific irradiation conditions. This study investigates the photon energies and angles of incidence for which the estimation of ERPG with the personal dose equivalents measured over and under the RPG (H_o and H_u) becomes more challenging. The energy and angular dependences of E_RPG, H_o and H_u were Monte Carlo calculated for photon exposures. The personal dosimeter of SCK-CEN was modeled and used to determine H_o and H_u. Different SD and DD algorithms were tested and critical exposure conditions were identified. Moreover, the influence of calibration methods was investigated for the SCK-CEN dosimeter when worn over RPG. We found that the accuracy with which E_RPG is calculated using SD and DD is strongly dependent on the energy and angle of incidence of photons. Also, the energy of the photon beam used to calibrate the H_o dosimeter can bias the estimation of E_RPG. (authors)

[en] The knowledge of effective dose can have a useful contribution to the optimization process of patient doses in vascular radiology and cardiology. For the determination of effective dose with computer codes like M.C.N.P. or M.C.N.P.-X, different available anthropomorphic phantoms were compared. In order to validate the calculations, the effective dose was also measured with the use of the Rando-Alderson (R.A.) phantom. Organ doses, normalized to the dose-area-product (D.A.P.), are calculated for an abdomen P.A. irradiation with a spectrum composed by 75 k Vp and 6.5 mm Al + 0.1 mm Cu. For 4 different phantoms: (1) the mathematical phantom B.O.D.Y.B.U.I.L.D.E.R.; (2) the voxel phantom M.A.X.; (3) a voxel model of the R.A.-phantom; (4) the experimental R.A. phantom. From these organ doses, effective doses were calculated of 0.151 mSv/Gy cm²; 0.141 mSv/Gy cm²; 0.295 mSv/mGy cm² and 0.245 mSv/Gy cm², respectively. We observed large differences between organ doses for the mathematical phantoms used frequently in the passed and the voxel models. The difference is smaller for the global effective dose factor. The organ doses were systematically higher for the Rando-Alderson phantom (experimental and calculated), compared to B.O.D.Y.B.U.I.L.D.E.R. and M.A.X.. (authors)

[en] In the neonatal intensive care units (NICU), premature new-borns may be exposed to important doses. Because of their increased radiosensitivity and longer life expectancy, dose optimisation is of importance. The present study aimed at evaluating the dose of the most common radiographs in the Belgian NICU. Entrance surface kerma (ESK) and kerma area product (KAP) were collected in 17 NICU (among 19 in Belgium). Median ESK ranged from 13 to 172 μGy and from 8 to 117 μGy for chest and combined chest-abdomen radiographs, respectively; median KAP ranged from 1.4 to 14.2 mGy cm² and from 3.8 to 28.1 mGy cm² for chest and combined chest-abdomen radiographs, respectively. Those differences were due to large variations in the examination settings. Diagnostic reference levels (DRL) were set for chest and combined chest-abdomen radiographs. Though the radiograph dose was usually low, the cumulative dose per stay could be high. The wide, intercentre differences indicate that there is scope for dose reduction. The use of DRL should contribute to achieve this object. (authors)

[en] This document presents dose measurements on patients in the field of interventional angiography. We have restricted this study to a common IR procedure, namely diagnostic angiography of the lower limbs. In this examination, radiographs are made over 6 adjoining standard regions from abdomen to feet. The RX tube is moved from one region to another under fluoroscopic guidance. To visualise the arteries, contrast media is injected through a catheter that has been inserted in the abdominal artery. The positioning of the catheter is also controlled by fluoroscopy. Only typical procedures (without medical complications) in male and female patients were considered in this study. Within the scope of the optimisation of patient doses, we looked for the influence of both the working procedure and the exposure parameters on patient dose. Examinations as performed by different operators and in different hospitals were included in the study. The effective dose E is calculated with the use of calculated derived conversion factors, which link practical dose measurements under well-defined conditions with estimates of the effective dose. Measurements in 4 different hospitals, 2 university hospitals and 2 peripheral hospitals are compared

[en] Ward staff in hospitals are often exposed to ionizing radiation from in-patients who have been injected by radiopharmaceuticals. Published data concerning this issue are mostly based on dose-rate measurements and occupancy factors. For this reason the Radiation Protection Office of the University Hospital of Brussel (UZ Brussel) started a study in order to assess the workaday reality concerning the external radiation dose. During 6 months 70 ward staff members were monitored during their daily tasks by means of thermoluminescent detectors (TLDs) that were attached on their hospital identification card. Additional TLDs where placed in various hospital and domestic locations to register different background levels. TLDs were calibrated in a secondary calibration laboratory. Calibrations were performed with the 250 keV ISO narrow X-ray spectrum. Simultaneously the activity and type of radiopharmaceutical entering the wards as well as individual workload of the staff members was recorded. Specific guidelines prevented loss of data and registration of exposures that where not job related. Despite the relatively high amount of activity entering in some wards, only 4 staff members received a dose that exceeds the significance level above the average background. Although the exposure to external radiation is very limited, additional exposures from radioactive contaminations can occur. The latter exposure pathway to ward staff could not be quantified during this study but can easily be avoided if the need for hygienic measures is emphasised. The results of this survey can help to encourage risk communication regarding the radiation exposure from nuclear medicine patients, which is presently nonexistent in many hospitals. This communication is extremely important to temper total indifference as well as radiophobia. (author)

[en] Lung disease represents one of the most life-threatening conditions in prematurely born children. In the evaluation of the neonatal chest, the primary and most important diagnostic study is therefore the chest radiograph. Since prematurely born children are very sensitive to radiation, those radiographs may lead to a significant radiation detriment. Hence, knowledge of the patient dose is necessary to justify the exposures. A study to assess the patient doses was started at the neonatal intensive care unit (NICU) of the Univ. Hospital in Leuven. Between September 2004 and September 2005, prematurely born babies underwent on average 10 X-ray examinations in the NICU. In this sample, the maximum was 78 X-ray examinations. For chest radiographs, the median entrance skin dose was 34 μGy and the median dose area product was 7.1 mGy.cm². By means of conversion coefficients, the measured values were converted to organ doses. Organ doses were calculated for three different weight classes: extremely low birth weight infants (<1000 g), low birth weight infants (1000-2500 g) and normal birth weight infants (>2500 g). The doses to the lungs for a single chest radiograph for infants with extremely low birth weights, low birth weights and normal birth weights were 24, 25 and 32 μGy, respectively. (authors)