Application of European protocol in the evaluation of contrast-to-noise ratio and mean glandular dose for two digital mammography systems

The performance of two digital mammography systems, Agfa CR75 and CRMM3 computed radiography (CR) and IMS Giotto MD direct digital radiography (DR), was assessed by applying a method recommended in the European protocol for quality control in mammography screening. The contrast-to-noise ratio (CNR) and mean glandular dose (MGD) values were measured and contrast detail (CD) analysis was performed. The CNRs for system CR were 21.9, 12.9, 9.5, 8.8, 7.4, 5.5 and 4.4 for 2, 3, 4, 4.5, 5, 6 and 7-cm polymenthylmethacrylate (PMMA) thickness, respectively. The respective CNRs for system DR were 10.4, 8.8, 6.3, 7.3, 7.2, 6.4 and 6.54. For the same phantom thickness sequence, the MGDs were 0.7, 1.1, 1.3, 1.6, 1.9, 2.5 and 3.4 mGy for system CR, whereas they were 0.7, 1.2, 1.1, 1.3, 1.8, 3.5 and 3.9 mGy for system DR. The CNR and MGD results satisfactorily correlate with CD analysis results. The MGD values compare well with the values recommended in the European protocol. Despite being simple, CNR and MGD can provide an effective system for performance assessment and constancy checks for related optimisations.     

Patient doses from screen-film and full-field digital mammography in a population-based screening programme

The aim of this study was to compare mean glandular dose (MGD) in all full-field digital mammography (FFDM) and screen film mammography (SFM) systems used in a national mammography screening program. MGD from 31 screening units (7 FFDM and 24 SFM), based on an average of 50 women at each screening unit, representing 12 X-ray models (6 FFDM and 6 SFM) from five different manufacturers were calculated. The MGD was significantly lower for FFDM compared with SFM (craniocaudal): 1.19 versus 1.27 mGy, respectively, mediolateral oblique: 1.33 versus 1.45 mGy, respectively), but not all of the FFDM units provided lower doses than the SFM units. Comparing FFDMs, the photon counting scanning-slit technology provides significantly lower MGDs than direct and indirect conversion digital technology. The choice of target/filter combination influences the MGD, and has to be optimised with regard to breast thickness.     

Mammography dosimetry using an in-house developed polymethyl methacrylate phantom

Phantom-based measurements in mammography are well-established for quality assurance (QA) and quality control (QC) procedures involving equipment performance and comparisons of X-ray machines. Polymethyl methacrylate (PMMA) is among the best suitable materials for simulation of the breast. For carrying out QA/QC exercises in India, a mammographic PMMA phantom with engraved slots for keeping thermoluminescence dosemeters (TLD) has been developed. The radiation transmission property of the developed phantom was compared with the commercially available phantoms for verifying its suitability for mammography dosimetry. The breast entrance exposure (BEE), mean glandular dose (MGD), percentage depth dose (PDD), percentage surface dose distribution (PSDD), calibration testing of automatic exposure control (AEC) and density control function of a mammography machine were measured using this phantom. MGD was derived from the measured BEE following two different methodologies and the results were compared. The PDD and PSDD measurements were carried out using LiF: Mg, Cu, P chips. The in-house phantom was found comparable with the commercially available phantoms. The difference in the MGD values derived using two different methods were found in the range of 17.5-32.6 %. Measured depth ranges in the phantom lie between 0.32 and 0.40 cm for 75 % depth dose, 0.73 and 0.92 cm for 50 % depth dose, and 1.54 and 1.78 cm for 25 % depth dose. Higher PSDD value was observed towards chest wall edge side of the phantom, which is due to the orientation of cathode-anode axis along the chest wall to the nipple direction. Results obtained for AEC configuration testing shows that the observed mean optical density (O.D) of the phantom image was 1.59 and O.D difference for every successive increase in thickness of the phantom was within±0.15 O.D. Under density control function testing, at -2 and -1 density settings, the variation in film image O.D was within±0.15 O.D of the normal density setting '0' and at +2 and +1 density setting, it was observed to be within±0.30 O.D. This study indicates that the locally made PMMA TLD slot phantom can be used to measure various mammography QC parameters which are essentially required for better outcomes in mammography.     

Evaluation of patient dose for mammography in Pernambuco, Brazil

The aim of this study is to evaluate the incident air kerma (INAK) and the mean glandular dose (MGD) during mammography in Recife, North-east Brazil. The study was performed in three institutions: a private clinic (A), a public hospital (B) and a private hospital (C). The incident air kerma to mammography procedures were estimated using a standard breast phantom and the patient MGD, evaluated in the units B and C, was performed using the calibration of output method. This method involves the recording of the patient exposure parameters (kVp, mAs, filter) and the measurement of these parameters of the incident air kerma using a calibrated ionisation chamber. The results obtained showed that INAK for the standard breast phantom, in the institutions A, B and C, were 18.2, 9.4 and 8.5 mGy, respectively. The results of patient MGD values ranged from 0.23 to 7.46 mGy per film, and the MGD values per woman were between 8.23 and 40.6 mGy for the C institution and between 1.50 and 18.78 mGy for the B institution.     

Implementation of the European protocol for quality control of the technical aspects of mammography screening in Bulgaria

The results from the national pilot project on implementation of the European protocol for the quality control (QC) of the technical aspects of mammography screening as well as the European protocol for dosimetry in mammography in Bulgaria are presented. A QC programme for mammography equipment and a standardised measurement protocol were created. The full QC programme was tested on four mammography units of different types and ages. A national survey was performed for entrance surface air kerma (ESAK) on 20 units using a 45 mm PMMA standard phantom. Average glandular dose (AGD) was calculated using the conversion coefficients from the European dosimetry protocol. The survey demonstrated considerable differences in the technical condition of the mammography units that resulted in varying image quality. The measured values of ESAK showed significant variations. Doses for approximately 45% of the units were found to be below the European reference level. The values for AGD ranged from 0.35 to 3.47 mGy. The main problems found were film processing, optical density (OD) control settings and AEC adjustment. The results showed the importance of film OD measurements parallel to dose measurements. The X-ray mammography in the country needs optimisation. Comprehensive quality assurance programme should be adopted in all departments covering permanent QC of the equipment, image quality and breast dose.     

Survey of mammography practice in Croatia: equipment performance, image quality and dose

A national audit of mammography equipment performance, image quality and dose has been conducted in Croatia. Film-processing parameters, optical density (OD), average glandular dose (AGD) to the standard breast, viewing conditions and image quality were examined using TOR(MAM) test object. Average film gradient ranged from 2.6 to 3.7, with a mean of 3.1. Tube voltage used for imaging of the standard 45 mm polymethylmethacrylate phantom ranged from 24 to 34 kV, and OD ranged from 0.75 to 1.94 with a mean of 1.26. AGD to the standard breast ranged from 0.4 to 2.3 mGy with a mean of 1.1 mGy. Besides clinical conditions, the authors have imaged the standard phantom in the referent conditions with 28 kV and OD as close as possible to 1.5. Then, AGD ranged from 0.5 to 2.6 mGy with a mean of 1.3 mGy. Image viewing conditions were generally unsatisfying with ambient light up to 500 lx and most of the viewing boxes with luminance between 1000 and 2000 cd per m(2). TOR(MAM) scoring of images taken in clinical and referent conditions was done by local radiologists in local image viewing conditions and by the referent radiologist in good image viewing conditions. Importance of OD and image viewing conditions for diagnostic information were analysed. The survey showed that the main problem in Croatia is the lack of written quality assurance/quality control (QA/QC) procedures. Consequently, equipment performance, image quality and dose are unstable and activities to improve image quality or to reduce the dose are not evidence-based. This survey also had an educational purpose, introducing in Croatia the QC based on European Commission Guidelines.     

A survey of the state of mammography practice in Bulgaria

The purpose of this work is to compare the state of a representative number of mammography systems in Bulgaria in terms of incident air kerma (IAK) and film optical density (OD) and to propose the optimisation measures where appropriate. IAK with a standard phantom and OD of the exposed films were measured on 22 % of all units in the country. IAK values ranged from 2 to 24.3 mGy, with the median being 7.9 mGy, first and third quartiles respectively being 5 and 11.2 mGy and the mean 8.6 mGy. OD values ranged from 0.5 to 2.4. Only 36 % of all units had OD within the recommended range. Only 27 % were satisfactorily set with OD within the recommended range and IAK below the third quartile. Full quality control (QC) measurements on 12 units showed a lot of problems. The observed big variations of IAK, with а factor of 12, are due to the non-optimised settings and film processing, the lack of standardisation and periodical QC. Corrective actions were recommended to optimise the settings of some systems and to improve the practice.     

Performance of mammography equipment in the Macedonian breast screening campaign 2008/2009

Breast screening campaign in Macedonia started in the end of 2007 and 19 national mammography departments were included. Contrary to the European Guidelines for Quality Assurance in Mammography Screening, the quality assurance activities were not implemented before the start of the campaign, except at the University Clinic of Radiology, Skopje. The quality control tests were performed for the very first time at 13 mammography units under a licence-obtaining procedure. One of the machines was suspended from clinical and screening practice due to heavy malfunction of the generator, X-ray tube and automatic exposure control (AEC) system. Only 3 of the 13 mammography machines met the criteria for tube voltage (kV) accuracy. Two of the seven AEC systems were calibrated in the optimal optical density (OD) range (OD >1.4). AEC settings corresponded to the recommendations at eight units, while nine units met basic overall image quality criteria. Mean glandular dose (MGD) was higher than the recommended level of 2.5 mGy in four departments. Mean gradient of the film G(0.25-2.0) was below 2.8 at four units. Only two light boxes had a luminance of >1700 cd m(-2) and six rooms had an ambient light level of <50 lx. The findings of this work clearly suggest that the performance of the mammography equipment involved in the campaign in almost 50 % do not supply basic quality criteria for a breast screening programme.     

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.     

Reference levels for image quality in mammography

Diagnostic reference levels are a well-established tool for optimisation in diagnostic radiology. A dose-reference level for certain diagnostic procedures, meant to identify practices with unusually high doses, is usually set at the third quartile of the distribution of doses in different diagnostic centres. If image quality is somehow quantified, the same 'worst quarter' principle can also be used to identify practices with less than optimal performance in terms of image quality. In Slovenia, the performance of mammographic centres is evaluated annually. Technical testing includes average glandular dose determination and evaluation of technical image quality using the image of a mammographic phantom. From the phantom image, simple image quality parameters are derived and for some of them reference levels can be established. In this study, the results from ten years of testing (1996-2006) at mammography centres are presented and the usefulness of reference levels is evaluated.     

Average glandular dose in routine mammography screening using a Sectra MicroDose Mammography unit

The Sectra MicroDose Mammography system is based on direct photon counting (with a solid-state detector), and a substantially lower dose to the breast than when using conventional systems can be expected. In this work absorbed dose measurements have been performed for the first unit used in routine mammography screening (at the Hospital of Helsingborg, Sweden). Two European protocols on dosimetry in mammography have been followed. Measurement of half value layer (HVL) cannot be performed as prescribed, but this study has demonstrated that non-invasive measurements of HVL can be performed accurately with a sensitive and well collimated solid-state detector with simultaneous correction for the energy dependence. The average glandular dose for a 50 mm standard breast with 50% glandularity, simulated by 45 mm polymethylmethacrylate, was found to be 0.21 and 0.28 mGy in March and December 2004, respectively. These values are much lower than for any other mammography system on the market today. It has to be stressed that the measurements were made using the current clinical settings and that no systematic optimisation of the relationship between absorbed dose and diagnostic image quality has been performed within the present study. In order to further increase the accuracy of absorbed dose measurements for this unit, the existing dose protocols should be revised to account also for the tungsten/aluminium anode/filter combination, the multi-slit pre-collimator device and the occurrence of a dose profile in the scanning direction.     

An estimate of the influence of the measurement procedure on patient and phantom doses in breast imaging

This work is aimed to study the variability of dosimetry results owing to various measurement methodologies for breast dosimetry. This is performed in the frame of the development of a national protocol for breast dosimetry. Doses for standard phantom and group of patients were calculated for two mammography systems from the tube output measured with a calibrated ionisation chamber. The backscatter from the phantom under the chamber contributes to an increase in dosimeter readings of approximately 0.8-1.5%, whereas the proximity of the compression plate to the chamber causes increase in the measured air kerma value by 6.5-7%. High value layer (HVL) measured with solid-state detector without corrections for energy dependence was 17% higher than the one measured with ionisation chamber, which causes corresponding overestimation of average glandular dose (AGD). The use of conversion factors based on typical but not measured HVL values leads to 3.5-5.6% overestimation of AGD. Although the sources of uncertainty were taken into account, the difference between the phantom and patient doses was 24%. Some practical recommendations to be included in the national dosimetry protocol are summarised.     

Evaluation of patient dose in some mammography centres in Iran

High diagnostic sensitivity and specificity while maintaining the least dose to the patient is the ideal mammography. The objective of this work was to evaluate patient dose and image quality of mammograms to propose corrective actions. The image quality for 1242 patient in 7 mammography facilities in Tehran city was evaluated based on selected image quality criteria using a three-point scale. Clinical image quality, the entrance surface air kerma, the average glandular dose and optical density of films for standard PMMA phantom of 4.5 cm thickness were evaluated. The results showed that up to 72 % of mammograms were in good condition to be diagnosed, and only about 3.4 % of the images were unacceptable or with suboptimal quality. The entrance surface air kerma values were in the range of 3.8-10.5 mGy, average glandular dose 0.5-1.8 mGy and optical density of films 0.74-2.03. The image quality evaluation after correction actions, periodic image quality evaluation and using the correct equipment certainly will improve patient dose.     

Volume computed tomography air kerma index and image quality evaluation in Brazil

The aim of this study was to evaluate the image quality of 29 computed tomography (CT) scanners in Brazil and to perform estimations of patient dose and image quality of common CT examinations at these equipment. The volume CT air kerma indexes (C(VOL)) were estimated, using normalised weighted air kerma indexes, supplied by the ImPACT group. The image quality tests were performed using the phantom and accreditation protocol from the American College of Radiology (ACR). The C(VOL) values for head scans varied between 8.7 and 108 mGy. The Hi-res chest examinations presented C(VOL) values varying from 0.4 to 32 mGy. For abdominal scans, the estimated C(VOL) values varied between 4.1 and 94 mGy. This wide variation of air kerma between different centres is related to the scanner type and also to the scanning parameters. The results also showed that the image quality did not attend all ACR CT accreditation requirements.     

Optimisation of X-ray examinations in Lithuania: start of implementation in mammography

Optimisation of medical X-ray examinations is very important for the enhancement of the reliability of the examination and for the reduction of the radiation dose to patients. Results of investigations of doses to patients during mammography using thermoluminescence dosemeters at different hospitals are presented together with a brief overview of the situation for mammography in Lithuania. It is shown that the entrance surface air kerma varies in a broad range and differed from hospital to hospital. Nevertheless the calculated values of average glandular dose (AGD) for a 'standard' breast being relatively high were comparable with those (3.2 mGy per exposure at net optical density 1.4) currently accepted by international authorities. Differences in AGD values evaluated at different hospitals demonstrate the existing potential for optimisation of the mammography screening procedures. The results of this investigation will be included in a database for patient doses in Lithuania and used for establishing a national reference dose level for mammography. Currently, reference levels recommended by international authorities are used in Lithuania.     

An overview of doses to patients and irradiation conditions of diagnostic chest x ray examinations carried out in hospitals of the City of São Paulo,Brazil

Recently the Brazilian health organisation published information conceming the number of hospitals, details of radiological equipment and frequency of medical examinations in the country. The information concerning the city of S?o Paulo is compiled here, complemented by a survey of absorbed doses to patients undergoing the most frequent examination: chest radiographs (postero-anterior (PA) and lateral (LAT) projections), as well as the physical parameters employed (tube voltage, current-time product, focus-film distance, field size). To collect the data, a sample of 12 hospitals (a representative sample of the 199 located in the city) was chosen, totalling 27 X ray machines. An anthropomorphic phantom was irradiated to simulate the patient. Absorbed doses were determined with thermoluminescence dosemeters placed in the phantom, externally and internally. Mean values of entrance surface dose (ESD) for PA and LAT projections were 0.22 mGy (from 0.07 to 0.61 mGy) and 0.98 mGy (from (1.30 to 4.01 mGy), respectively. The average organ doses per complete examination (PA and LAT) were 0.15 and 0.24 mGy to thyroid and lung, respectively. The thyroid was thus in the primary beam in many cases. The large variation in the ESD and organ doses indicates that much can be done in order to reduce the patient doses by adequate changes of physical parameters, without loss of image quality.     

Towards a proposition of a diagnostic (dose) reference level for mammographic acquisitions in breast screening measurements in Belgium

A diagnostic reference level (DRL) is a dose level for a typical X-ray examination of a group of patients with standard body sizes and for broadly defined types of equipment. These levels are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied. In this paper, we have calculated DRLs for screening mammography in Belgium. The 95th percentile of the mean average glandular dose is 2.46 mGy. The DRL based on polymethyl methacrylate (PMMA) measurements was 2.08 mGy. Correlation coefficient (R) between doses from patient studies and phantom studies was 0.90, with an average underestimation of the phantom measurements of 15% for systems that use only Mo/Mo anode/filter. For the centres that use other anode/filters, there is not enough scientific evidence that a single phantom measurement of a standard PMMA block is representative for the patient dose.     

Measurement of the radiation dose and assessment of the risk in mammography screening for early detection of cancer of the breast, in Israel

The mean glandular doses to samples of women attending for mammographic screening are measured routinely at screening centres in Israel. As at present, no detailed and systematic data have been collected regarding the average glandular dose in mammography screening procedures carried out in Israel for the last 20 y. Especially data are lacking related to the glandular dose (GD) involved in mammography with the new digital mammography systems. In this work, partial results of the measurements are presented to asses the radiation dose to the breast and to the glandular tissue within the Israeli national mammography programme updated to year 2009.     

Influence of the rotation centre in panoramic radiography

The aim is to present the curve of the rotation centre in dental panoramic radiography and to examine its influence on organ doses. A screenless film was fixed between the layers of an Alderson Rando phantom in the centre of the mandible. The phantom was positioned in two different X-ray units [Scanora (Soredex, Helsinki, Finland) and Orthophos (Sirona, Bensheim, Germany)] and exposed. Organ doses and effective doses were determined. The curves of the rotation centre showed clear differences especially in the area of the parotid gland. These differences corresponded to the differences in organ doses and in effective doses (Scanora: 29.9 microGy; Orthophos Plus: 14 microGy). Artefacts might be shown (Orthophos, result of a plate osteosynthesis) or not (Scanora) due to the different rotation centres. Differences in organ doses and in image quality, e.g. artefacts, were explained with the curve of the rotation centre and beam geometry.     

A high-resolution voxel phantom of the breast for dose calculations in mammography

Though mammography is one of the most sensitive methods to detect breast cancer, the benefit of the mammography screening programmes is still not clearly proven. One of the reasons is the radiation dose delivered by the examinations. Simulations of the radiation transport based on realistic breast phantoms are a useful tool to estimate the dose for the risk relevant parenchymal tissue. Specimens of real breasts have been fixated using a specially designed process while being compressed as in mammography. They have been scanned using the high-resolution mode of a CT. A segmentation has been carried out by assigning the voxels to different tissues. The resulting voxel phantom allows the assessment of tissue doses by Monte-Carlo calculations and can be used to simulate the diagnostic outcome of different imaging procedures. Three different tissues were separated: skin, adipose and 'breast tissue'. This allows reasonable calculations of the average glandular doses in mammography.