Establishing the European diagnostic reference levels for interventional cardiology.

Interventional cardiac procedures may be associated with high patient doses and therefore require special attention to protect the patients from radiation injuries such as skin erythema, cardiovascular tissue reactions or radiation-induced cancer. In this study, patient exposure data is collected from 13 countries (37 clinics and nearly 50 interventional rooms) and for 10 different procedures. Dose data was collected from a total of 14,922 interventional cardiology procedures. Based on these data European diagnostic reference levels (DRL) for air kerma-area product are suggested for coronary angiography (CA, DRL = 35 Gy cm2), percutaneous coronary intervention (PCI, 85 Gy cm2), transcatheter aortic valve implantation (TAVI, 130 Gy cm2), electrophysiological procedures (12 Gy cm2) and pacemaker implantations. Pacemaker implantations were further divided into single-chamber (2.5 Gy cm2) and dual chamber (3.5 Gy cm2) procedures and implantations of cardiac resynchronization therapy pacemaker (18 Gy cm2). Results show that relatively new techniques such as TAVI and treatment of chronic total occlusion (CTO) often produce relatively high doses, and thus emphasises the need for use of an optimization tool such as DRL to assist in reducing patient exposure. The generic DRL presented here facilitate comparison of patient exposure in interventional cardiology.

A Holistic Approach to Assessment of Population Exposure to Radiation: Challenges and Initiatives of a Regulatory Authority.

A regulatory authority for radiation safety should continuously evaluate and improve the national safety framework, in line with current requirements and standards. In this context, the Greek Atomic Energy Commission initiated a series of concerted actions. The radiation dose to the population due to public and medical exposures was assessed. The assessment of dose due to public exposure was based on measurements of radon concentrations in dwellings, radionuclide concentrations in environmental samples, and air dose rates; the assessment of dose due to medical exposure was based on dose measurements for typical examinations or procedures and data on their frequency. The mean effective dose to a member of the population was found to be 4.5 mSv (1.8 mSv and 2.7 mSv from medical and public exposures, respectively). Regarding occupational exposure, aircrew dose assessment, eye lens monitoring, and the national dose registry were significantly improved. With respect to artificial tanning (sun beds), the ultraviolet radiation produced was assessed and the practices followed were observed. Results demonstrated exceedance of the 0.3 W m erythema effective irradiance limit set in European Union standards by 63.5% of the sun beds measured, along with general noncompliance with standards. An overarching activity was the upgrade of the Greek Atomic Energy Commission information system in order to collect and disseminate radiation data electronically, launch a networking strategy for interaction with stakeholders, and facilitate the process of regulatory control. In response to the above findings, regulatory actions have been initiated.

On the total system error of a robotic radiosurgery system: phantom measurements, clinical evaluation and long-term analysis.

The total system error (TSE) of a CyberKnife® system was measured using two phantom-based methods and one patient-based method. The standard radiochromic film (RCF) end-to-end (E2E) test using an anthropomorphic head and neck phantom and isocentric treatment delivery was used with the 6Dskull, Fiducial and Xsight® spine (XST) tracking methods. More than 200 RCF-based E2E results covering the period from installation in 2006 until 2017 were analyzed with respect to tracking method, system hardware and software versions, secondary collimation system, and years since installation. An independent polymer gel E2E method was also applied, involving a 3D printed head phantom and multiple spherical target volumes widely distributed within the brain. Finally, the TSE was assessed by comparing the delineated target in the planning computed tomography images of a patient treated for a thalamic functional target with the radiation-induced lesion defined on the six-month follow-up magnetic resonance (MR) images. Statistical analysis of the RCF-based TSE results showed mean ± standard deviation values of 0.40 ± 0.18 mm, 0.40 ± 0.19 mm, and 0.55 ± 0.20 mm for the 6Dskull, Fiducial, and XST tracking methods, respectively. Polymer gel TSE values smaller than 0.66 mm were found for seven targets distributed within the brain, showing that the targeting accuracy of the system is sustained even for targets situated up to 80 mm away from the center of the skull. An average clinical TSE value of 0.87 ± 0.25 mm was also measured using the FSE T2 and FLAIR post-treatment MR image data. Analysis of the long-term RCF-based E2E tests showed no changes of TSE over time. This study is the first to report long-term (>10 years) analysis of TSE, TSE measurement for targets positioned at large distances from the virtual machine isocenter, or a clinical assessment of TSE for the CyberKnife system. All of these measurements demonstrate TSE consistently < 1 mm.

Establishment of diagnostic reference levels for dental panoramic radiography in Greece.

The purpose of the present study was to present the national diagnostic reference levels (DRL) established for panoramic dental examinations in Greece. The establishment of DRL, as a tool for the optimisation of radiological procedures, is a requirement of national regulations. Measurements performed by the Greek Atomic Energy Commission on 90 panoramic systems have been used for the derivation of DRL values. DRL values have been proposed for exposure settings of different patient types (child, small adult and standard adult), both for film and digital imaging. The DRLs for different patient types are grouped in three categories: children, small adults (corresponding to female) and average adults (corresponding to male). Proposed DRLs for these groups are 2.2, 3.3 and 4.1 mGy, respectively. In order to investigate the correlation of DRLs with the available imaging modalities (CR, DR and film), this parameter was taken into account. DR imaging DRL is the lowest at 3.5 mGy, CR imaging the highest at 4.2 mGy and film imaging at 3.7 mGy. In order to facilitate comparison with other studies, kerma-width product values were calculated from Ki, air and field size.

Diagnostic reference levels and patient doses in computed tomography examinations in Greece.

The purpose of this study is to present a national survey that was performed in Greece for the establishment of national Dose Reference Levels (DRLs) for seven common adult Computed Tomography (CT) examinations. Volumetric computed tomography dose index and dose-length product values were collected from the post-data page of 65 'modern' systems that incorporate tube current modulation. Moreover, phantom dose measurements on 26 'older' systems were performed. Finally, the effective dose to the patient from a typical acquisition during these examinations was estimated. The suggested national DRLs are generally comparable with respective published values from similar European studies, with the exception of sinuses CT, which presents significantly higher values. This fact, along with the large variation of the systems' dose values that were observed even for scanners of the same type, indicates a need for further patient protection optimisation without compromising the clinical outcome.

Establishment of diagnostic reference levels for dental intraoral radiography.

Diagnostic reference levels (DRLs) is a tool for the optimisation of radiological procedures. Establishment of a DRL is a requirement of national regulations. Measurements performed by the Greek Atomic Energy Commission on 529 dental intraoral radiographic facilities have been used in order to define DRLs for digital and film imaging modalities, taking into account the region of the mouth to be imaged. Thus, different DRL values have been proposed for minimum (usually incisors), maximum (usually maxillary molars) and average exposure settings, both for film and digital imaging. The results have been compared with similar studies performed in Europe and the USA and are in line with the most recent ones.

Comparison of full field digital (FFD) and computed radiography (CR) mammography systems in Greece.

The purpose of this study is to evaluate and compare the performance of 52 full field digital (FFD) and computed radiography (CR) mammography systems checked by the Greek Atomic Energy Commission with respect to dose and image quality. Entrance surface air kerma (ESAK) was measured and average glandular dose (AGD) was calculated according to the European protocol on dosimetry in mammography. The exposures were performed using the clinical protocol of each laboratory. The image quality was assessed by the total score of resolved phantom structures incorporated in an American College of Radiology accreditation phantom. The mean ESAK values for FFD and CR systems were 4.59 ± 1.93 and 5.0 ± 1.78 mGy, respectively, whereas the AGD yielded a mean value of 1.06 ± 0.36 mGy for the FFD and 1.04 ± 0.35 mGy for the CR systems. Considering image quality, FFD systems indicated a mean total score of 13.04 ± 0.89, whereas CR systems a mean total score of 11.54 ± 1.06.

Image quality and patient dose in computed tomography examinations in Greece.

The purpose of this study is to evaluate image quality of various computed tomography (CT) scanners installed in Greece, as well as to investigate patient doses from common CT examinations. An image quality survey was performed in 44 CT scanners countrywide. The imaging performance of the systems was evaluated by measurements of certain parameters, such as image noise, spatial uniformity, high- and low-contrast resolution and slice thickness accuracy. Moreover, preliminary results of patient dose survey are presented. Concerning image quality, 80 % of the scanners were found to be in compliance with the national legislation and relative international guidelines for all the examined parameters. Weighted CT dose index and dose-length product values for chest and abdomen routine examinations were generally below the dose reference levels (DRLs) suggested by the European Commission. However, some scanners were found to deliver significantly higher doses than the suggested DRL for head routine examinations. Finally, differences in the performance among scanners of the same type and similar age were observed, pointing out the importance of frequent calibration, routine quality control and proper maintenance.

Determination of the diagnostic x-ray tube practical peak voltage (PPV) from average or average peak voltage measurements.

The practical peak voltage (PPV) has been adopted as the reference measuring quantity for the x-ray tube voltage. However, the majority of commercial kV-meter models measure the average peak, U(P), the average, U, the effective, U(eff) or the maximum peak, U(P) tube voltage. This work proposed a method for determination of the PPV from measurements with a kV-meter that measures the average U or the average peak, U(p) voltage. The kV-meter reading can be converted to the PPV by applying appropriate calibration coefficients and conversion factors. The average peak k(PPV,kVp) and the average k(PPV,Uav) conversion factors were calculated from virtual voltage waveforms for conventional diagnostic radiology (50-150 kV) and mammography (22-35 kV) tube voltages and for voltage ripples from 0% to 100%. Regression equation and coefficients provide the appropriate conversion factors at any given tube voltage and ripple. The influence of voltage waveform irregularities, like 'spikes' and pulse amplitude variations, on the conversion factors was investigated and discussed. The proposed method and the conversion factors were tested using six commercial kV-meters at several x-ray units. The deviations between the reference and the calculated-according to the proposed method-PPV values were less than 2%. Practical aspects on the voltage ripple measurement were addressed and discussed. The proposed method provides a rigorous base to determine the PPV with kV-meters from U(p) and U measurement. Users can benefit, since all kV-meters, irrespective of their measuring quantity, can be used to determine the PPV, complying with the IEC standard requirements.

The use of active personal dosemeters as a personal monitoring device: comparison with TL dosimetry.

The use of active personal dosemeters (APDs) not only as a warning device but also, in some cases, as an official and hence stand-alone dosemeter is rapidly increasing. A comparison in terms of dose, energy and angle dependence, among different types of APD and a routinely used whole-body thermoluminescence dosemeter (TLD) has been performed. Significant differences were found between the TLD readings and mainly some not commonly used APDs. The importance of choosing the best adapted APD according to the radiation field characteristics is pointed out.

The effect of a compression paddle on energy response, calibration and measurement with mammographic dosimeters using ionization chambers and solid-state detectors.

A compression paddle is always used in mammography x-ray examinations, in order to improve image quality and reduce patient doses. Although clinical dose measurements should be performed with the paddle to interfere with the x-ray beam, calibration of mammography dosimeters is performed free in air without the presence of the paddle. The paddle hardens the x-ray beam, which has an impact on a dosimeter performance, particularly on high-energy-dependent detectors. Due to the paddle, clinical mammography x-ray systems may exhibit beams with HVL values exceeding those of the IEC 61267 RQR-M series qualities at which dosimeters are usually calibrated. In this study, the influence of the paddle in mammography dosimetry is examined, in Mo/Mo anode/filter x-ray qualities. PMMA slabs of 1, 2 and 3 mm thickness and Al foils of 0.05, 0.10 and 0.15 mm thicknesses were used to simulate the paddles, producing beams with HVL values from 0.28 up to 0.43 mmAl. In these qualities, four solid-state (ST) detectors and three ionizations chambers (IC) were calibrated in terms of Kair and N(K) and k(Q) were deduced. The results showed that all IC and two modern-type ST dosimeters have a flat energy response in the above HVL range (less than 3%), so their calibration factor at RQR-M2 quality could be safely used for clinical measurements. Two other ST dosimeters exhibit up to 20% energy response, so differences up to 15% in dose measurement may be observed if the effect of paddle on their performance is ignored. Finally, the need of additional mammographic calibration qualities to the existing IEC 61267 RQR-M series is examined and discussed.

Image quality evaluation and patient dose assessment of medical fluoroscopic X-ray systems: a national study.

This study presents the results from a survey conducted by the Greek Atomic Energy Commission (GAEC), during the period 1998-2003, in 530 public and private owned fluoroscopic X-ray systems in Greece. Certain operational parameters for conventional and remote control systems were assessed, according to a quality control protocol developed by GAEC on the basis of the current literature. Public (91.5%) and private (81.5%) owned fluoroscopic units exhibit high-contrast resolution values over 1 lp mm(-1). Moreover, 88.5 and 87.1% of the fluoroscopic units installed in the public and private sector, respectively, present Maximum Patient Entrance Kerma Rate values lower than 100 mGy min(-1). Additionally, 68.3% of the units assessed were found to perform within the acceptance limits. Finally, the third quartile of the Entrance Surface Dose Rate distribution was estimated according to the Dose Reference Level definition and found equal to 35 mGy min(-1).

Performance of medical radiographic X-ray systems in Greece for the time period 1998-2004.

This study presents the results of the on-site inspections performed by the Greek Atomic Energy Commission (GAEC) on conventional X-ray systems, both in public and private medical radiology departments. A part of the inspection concerns the assessment of important radiographic parameters obtained according to a specified quality control protocol and the comparison of the measured parameter values with the corresponding acceptance limits. A total number of 1011 radiographic systems were inspected by the GAEC during the period 1998-2004, with 63.4% of them being privately owned. Analysis of 8 different operational parameters is carried out providing information on the overall performance, as well as on each parameter of the inspected X-ray systems. Tube voltage reproducibility values show the highest percentage of acceptability (98.9%, 99.5% for private and public owned radiographic systems respectively), while linearity of radiation output for private systems (72.5%) and time accuracy for public ones (72.7%) show the worst results. The comparison of the results for the private sector to those of a similar study carried out during the period 1995-1997 indicates a substantial improvement in X-ray systems performance. Higher level of improvement shows exposure time accuracy (12.2% percentile increase) and linearity of radiation output (12.5% percentile increase). Nevertheless, the situation can be further optimized if maintenance and quality control of the radiographic systems are carried out on a more regular basis.

Calibration, performance and type testing of personal dosemeters used in ionising-radiation applications in Greece.

Active Personal Dosemeters (APDs) are widely used in real-time personal dosimetry. Their performance, operational characteristics and limitations, as well as their calibration should be routinely checked to assure satisfactory operation and safe use. This study summarises the results of such type tests and calibrations performed in almost 4750 dosemeters at Ionising Radiation Calibration Laboratory (HIRCL) of Greek Atomic Energy Commission (GAEC). About 13.8% of the pencil type and 4.3% of the electronic dosemeters were found to be out of limits of acceptable performance. For the pencil type dosemeters, the mean calibration factor (CF+/-SD) for high- and low-dose categories was found to be 1.014+/-0.102 (range 0.793-1.458) and 0.995+/-0.059 (range 0.794-1.311), respectively. Of these >85% of them had reproducibility better than 90%, while <1% showed remarkable non-linearity and approximately 10% of them failed to retain the dose reading within the limits after 24 h. For the electronic dosemeters, the mean CF was 1.034+/-0.046 (range 0.967-1.238). The majority of them showed good reproducibility and linearity results while, after irradiation, the dose readings were not shifted through time. The energy response varies with the dosemeter type, reaching in one dosemeter type down to 50%. Both electronic and pencil did not showed electronic equilibrium problems.

Comparison of radiation shielding requirements for HDR brachytherapy using 169Yb and 192Ir sources.

169Yb has received a renewed focus lately as an alternative to 192Ir sources for high dose rate (HDR) brachytherapy. Following the results of a recent work by our group which proved 169Yb to be a good candidate for HDR prostate brachytherapy, this work seeks to quantify the radiation shielding requirements for 169Yb HDR brachytherapy applications in comparison to the corresponding requirements for the current 192Ir HDR brachytherapy standard. Monte Carlo simulation (MC) is used to obtain 169Yb and 192Ir broad beam transmission data through lead and concrete. Results are fitted to an analytical equation which can be used to readily calculate the barrier thickness required to achieve a given dose rate reduction. Shielding requirements for a HDR brachytherapy treatment room facility are presented as a function of distance, occupancy, dose limit, and facility workload, using analytical calculations for both 169Yb and 192Ir HDR sources. The barrier thickness required for 169Yb is lower than that for 192Ir by a factor of 4-5 for lead and 1.5-2 for concrete. Regarding 169Yb HDR brachytherapy applications, the lead shielding requirements do not exceed 15 mm, even in highly conservative case scenarios. This allows for the construction of a lead door in most cases, thus avoiding the construction of a space consuming, specially designed maze. The effects of source structure, attenuation by the patient, and scatter conditions within an actual treatment room on the above-noted findings are also discussed using corresponding MC simulation results.

Occupational exposure in Greek industrial radiography laboratories (1996-2003).

More than 40 industrial radiography laboratories are operating in Greece using X-ray or gamma-ray sources and more than 250 workers occupationally exposed to ionising radiation in these facilities are monitored on a regular basis. This study presents the evolution of individual doses received by radiographers during the past years. The mean annual dose (MAD) of all workers as well as of exposed workers is estimated, and correlated to the types of laboratories and practices applied. The MAD of the exposed workers in industrial radiography is compared with the doses of workers in other specialties and with the doses of radiographers in other countries. Furthermore, the study attempts to propose dose constraints for the practices in industrial radiography, according to the BSS European directive and the relevant Greek radiation protection legislation. The proposed value was defined as the dose below which the annual doses of 75% of the exposed radiographers are expected to be included.

Calibration of dosemeters used in mammography with different X ray qualities: EUROMET project no. 526.

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrated.

From films to thermoluminescence dosemeters: the Greek Atomic Energy Commission experience.

The personnel dosimetry department of the Greek Atomic Energy Commission (GAEC) assures the individual monitoring of almost 8000 occupationally exposed workers. Thermoluminescence dosimetry systems will replace the existing photographic dosimetry system for the individual monitoring with the joint support of IAEA and GAEC. The thermoluminescence dosimetry system consists of two automated readers, one automated irradiator and about 20,000 dosemeters purchased from the Rados Co. The properties of two thermoluminescent materials have been compared: LiF has been chosen for the whole-body dosemeter configuration and Li2B4O7 for the extremities. The technical evaluation of the system has been performed according to the European and IEC standards. The overall uncertainty has been calculated. The existing database system, and the accounting and dispatching procedures have been adapted to the new demands. The system became operational on March 2000, and the official distribution of thermoluminescence dosemeters has begun.

Estimation of doses received by patients undergoing radiological examinations in Greece.

This study deals with the estimation of doses received by patients undergoing radiological examinations in order to establish diagnostic reference levels (DRLs) within the process of optimisation of patients' exposure in Greece. Six large hospitals in Athens were selected and 385 patients made up the sample. The entrance surface doses (ESDs) to patients undertaking five common X ray examinations (chest, cervical spine, lumbar spine AP and LAT, pelvis) were estimated using both thermoluminescence dosemeters (TLDs) attached to the patient's skin and an ionisation chamber for air kerma measurements. Exposure settings and patient's data were recorded. Results concerning the kilovoltage and focus-to-film-distance (FFD) settings and the ESD values were analysed and compared to those recommended by the EU. Discrepancies in the patient doses and techniques used for the examinations studied were found among the different hospitals denoting the importance of establishing a national quality assurance programme and examination protocols to ensure patient doses are kept as low as possible. All the examinations studied fulfilled the EU recommendations except that for the chest where the doses were considerably higher due to the use of low kVP settings.

Examination frequencies and patient doses from computed tomography examinations in the area of Athens, Greece.

A survey was conducted in the Athens region between the years 1996-1997, in which 33 CT scanner facilities from the 67 operating in this area participated. Examination frequencies from the 33 scanners were 187,875 per year for all types of examinations. Using published estimations for the mean effective dose for each type of examination, it was estimated that the collective dose from the above examinations was about 1,100 person-Sv, which, if projected to the total number of 152 CT scanners operating in Greece at the time of the survey, results in about 0.5 mSv per caput dose each year for the Greek population, which is probably the highest in Europe.