Position paper: recommendations for a digital mammography quality assurance program V4.0.

In 2001 the ACPSEM published a position paper on quality assurance in screen film mammography which was subsequently adopted as a basis for the quality assurance programs of both the Royal Australian and New Zealand College of Radiologists (RANZCR) and of BreastScreen Australia. Since then the clinical implementation of digital mammography has been realised and it has become evident that existing screen-film protocols were not appropriate to assure the required image quality needed for reliable diagnosis or to address the new dose implications resulting from digital technology. In addition, the advantages and responsibilities inherent in teleradiology are most critical in mammography and also need to be addressed. The current document is the result of a review of current overseas practice and local experience in these areas. At this time the technology of digital imaging is undergoing significant development and there is still a lack of full international consensus about some of the detailed quality control (QC) tests that should be included in quality assurance (QA) programs. This document describes the current status in digital mammography QA and recommends test procedures that may be suitable in the Australasian environment. For completeness, this document also includes a review of the QA programs required for the various types of digital biopsy units used in mammography. In the future, international harmonisation of digital quality assurance in mammography and changes in the technology may require a review of this document. Version 2.0 represented the first of these updates and key changes related to image quality evaluation, ghost image evaluation and interpretation of signal to noise ratio measurements. In Version 3.0 some significant changes, made in light of further experience gained in testing digital mammography equipment were introduced. In Version 4.0, further changes have been made, most notably digital breast tomosynthesis (DBT) testing and QC have been addressed. Some additional testing for conventional projection imaging has been added in order that sites may have the capability to undertake dose surveys to confirm compliance with diagnostic reference levels (DRLs) that may be established at the National or State level. A key recommendation is that dosimetry calculations are now to be undertaken using the methodology of Dance et al. Some minor changes to existing facility QC tests have been made to ensure the suggested procedures align with those most recently adopted by the Royal Australian and New Zealand College of Radiologists and BreastScreen Australia. Future updates of this document may be provided as deemed necessary in electronic format on the ACPSEM's website ( https://www.acpsem.org.au/whatacpsemdoes/standards-position-papers and see also http://www.ranzcr.edu.au/quality-a-safety/radiology/practice-quality-activities/mqap ).

Technical developments in radiology in Australasia dating from 1977.

This article outlines the enormous technological advances that have taken place in the practice of radiology in Australasia in the 30 years since approximately 1977. These developments have led to significant improvements in image quality across all modalities, including even general radiography, which had as its genesis Roentgen's ground-breaking discovery of X-rays in 1895. However, nowhere has the development been more dramatic than in magnetic resonance imaging (MRI). This may be brought into stark reality by noting that the first MRI image of a human finger was produced in 1976 followed one year later by that of a human chest and the first MRI units were not installed in Australia and New Zealand until 1986 and 1991, respectively. The quality of these early images would be judged as laughable by today's standards where the impressive isotropic imaging that can be achieved at sub-millimetre level by both MRI and CT could not have been dreamed of 30 years ago. The review also highlights some challenges for the future of the medical physics profession.

Interim recommendations for a digital mammography quality assurance program.

In 2001 the ACPSEM published a position paper on quality assurance in screen film mammography which was subsequently adopted as a basis for the quality assurance programs of both the Royal Australian and New Zealand College of Radiologists (RANZCR) and of BreastScreen Australia. Since then the clinical implementation of digital mammography has been realised and it has become evident that existing screen-film protocols were not appropriate to assure the required image quality needed for reliable diagnosis or to address the new dose implications resulting from digital technology. In addition, the advantages and responsibilities inherent in teleradiology are most critical in mammography and also need to be addressed. The current document is the result of a review of current overseas practice and local experience in these areas. At this time the technology of digital imaging is undergoing significant development and there is still a lack of full international consensus about some of the detailed Quality Control tests that should be included in quality assurance (QA) programs. This document describes the current status in digital mammography QA and recommends test procedures that may be suitable in the Australasian environment. For completeness, this document also includes a review of the QA programs required for the various types of digital biopsy units used in mammography. In the future, international harmonisation of digital quality assurance in mammography and changes in the technology may require a review of this document. Accordingly, updates of this document will be provided as deemed necessary in electronic format on the ACPSEM's website (see http://www.acpsem.org.au/au/subgroup/radiology/RadiologySG_index.html).

Importance in optimization of multi-slice computed tomography scan protocols.

This paper reviews the reasons why multi-slice CT scanners may give patients higher dose than their single-slice predecessors and discusses the type of optimization of multi-slice scan protocols that may be undertaken to keep patient doses to acceptable levels without compromising image quality. It also provides estimates of patient effective dose values and dose length products for typical procedures and briefly discusses the implication that these dose values have for the induction of possible stochastic effects.

Recommendations for a technical quality control program for diagnostic X-ray equipment.

This position paper was produced by a working party set up by the Radiology Special Interest Group of the ACPSEM in 2001. It is designed to give the consensus view of College members in Australia and New Zealand on the nature and frequency of tests which should be performed on diagnostic x-ray equipment to maintain adequate quality control of imaging performance and radiation safety. Tests on mammographic equipment have been excluded having been covered in a previous ACPSEM position paper (Australas Phys Eng Sci Med, 24(3):107-131, 2001). Detailed descriptions of test procedures are not given but it is intended that a series of workbooks should be produced giving College recommended test methods for each imaging modality. The recommendations are produced here in an easy-to-read, tabular form giving the nature and purpose of each test and the implications of non-compliance with regard to image quality and radiation safety.

Patient doses in multi-slice CT and the importance of optimisation.

Substantive surveys of patient doses arising from CT examinations have been conducted in our Hospital. In the first instance doses were measured on a single-slice Siemens Plus 4 scanner. A similar survey was conducted initially following commissioning of a Siemens multi-slice Sensation scanner and subsequently after some effort was made to optimise scanning protocols. Doses are reported in terms of dose-length products (DLPs) and as effective doses. The optimisation process on the multi-slice scanner resulted in a reduction in DLP values by between 14% and 58%. With two exceptions, significantly lower or comparable DLP values were obtained when meaningful comparisons were made with results previously obtained with the single-slice scanner. Specific results for the multi-slice scanner in terms of the median DLP in mGy.cm (and median effective dose in mSv) are: routine brain, 660 (1.5); routine chest, 195 (4.0); chest with portal liver phase, 370 (7.2); routine chest with high resolution component, 250 (5.1); chest/abdomen/pelvis with contrast, 560 (11.0); routine abdomen without contrast, 145 (2.4); routine abdomen with contrast 215 (3.6); routine abdomen/pelvis without contrast, 230 (4.4); routine abdomen/pelvis with contrast, 345 (6.3); abdomen/pelvis triple phase, 715 (13.3); renal scan, 260 (4.6); lumbar spine, 445 (7.2); cerebral angiography, 240 (0.58); pulmonary angiography, 165 (3.4); aortic angiography, 305 (5.7). Based on the survey findings possible values for CT examination local diagnostic reference levels (LDRLs) are suggested.

A comparison of mammography spectral measurements with spectra produced using several different mathematical models.

Due to the relatively complex nature of spectral measurements from x-ray machines, many researchers use mathematical models to simulate the spectra they need. However, there is concern over their accuracy, and hence the impact that their accuracy may have, on subsequent calculations that rely upon the spectra modelled. With this in mind spectral measurements have been performed on a mammography machine and a comparison with spectra calculated using several different models is presented. Several different techniques have been investigated in the spectral measurements to allow for pulse pileup and other effects of high count rate. Comparison with half value layer (HVL) measurements shows that the use of a gating signal in conjunction with the air-free path provides accurate results without the need for a pinhole collimator. Comparison of the measured spectra with those calculated using different models proposed in the literature suggests that accurate results can be produced by all models, but only if the user attempts to match the calculated HVL of the modelled spectrum with the physically measured HVL. If this is not done the modelled spectra may be in error. The impact of such an error is demonstrated in calculations of mean glandular dose, which indicate a possible underestimate of the dose by up to 20%.

Recommendations for a mammography quality assurance program.

In 1989 the ACPSEM published a position paper entitled "A Quality Assurance Programme for Mass Screening in Mammography". This paper described test parameters and performance specifications for the equipment related aspects of a mammography quality assurance program. Advice on test equipment selection was also provided. In the intervening period of time there have been considerable advances in mammography technology creating a need to review a number of the paper's recommendations. There have also been considerable developments in the mammography quality assurance (QA) field, not the least of which includes the American College of Radiology Mammography Accreditation Program (ACR-MAP) and the similarly structured Royal Australian and New Zealand College of Radiologists' Mammography Accreditation Program (RANZCR-MAP). In light of these developments it was decided by the Radiology Interest Group to review the ACPSEM position on those aspects of mammography QA that fall within the medical physicist's area of expertise. This document represents the outcome of those deliberations.

Radiation doses from common radiographic procedures: a ten year perspective.

Using a semi-empirical model patient doses for a number of plain film radiographic procedures following the implementation of Computed Radiography (CR) technology in our Hospital have been evaluated. The results are presented in terms of the entrance surface dose (ESD) and the effective dose. A comparison of these results, with those reported previously for 1988, suggests that with the exception of chest radiography, patient doses have decreased although in many instances the decreases are not statistically significant. The finding for chest examinations stands apart from all others in that the introduction of CR technology has resulted in a substantial increase in patient dose for the PA view by at least 18%. The major reason for these apparently contradictory findings has its roots in the effectively variable speed of CR systems and the willingness of radiologists to accept more noise in some CR images.

An investigation into the impact of anatomical variation upon mean glandular dose produced within a standard breast.

By using the EGS4 Monte Carlo computer program the normalised mean glandular dose (MGD) was calculated for a breast model that is intended to reflect the composition of an "average" breast. The reliability of the calculation was established by comparing the predictions with previously published values for a breast model. The breast model used was then altered in order to reflect the possible extremes in glandular distribution that could occur within a compressed breast. These results show that the MGD could vary by up to a factor of four depending upon where the majority of glandular tissue is located within the breast. The impact of this variation in MGD upon risk assessment within mammography is then discussed.

Determination of correct AEC function with computed radiography cassettes.

It has long been recognized that the assessment of Automatic Exposure Control (AEC) function is an important criterion in the assessment of any general radiographic x-ray installation. Of the tests commonly performed on an AEC, only Beam Quality Dependence relates intimately with the optical density produced on the resultant radiograph. In this test the AEC function is ascertained as being satisfactory or otherwise, on the basis of whether the optical density on the radiograph is controlled within well defined limits. With computed radiography (CR), where the conventional screen-film combination is replaced by a storage phosphor screen, the process by which the digital image is presented on film restricts the resultant optical densities to an extremely tight range, independent of the air kerma incident upon the CR phosphor plate. The implication of this is that the measurement of optical density can not be used as a direct measure of AEC function, and a test such as Beam Quality Dependence cannot be performed in the conventional manner. To overcome this, the relationship between incident air kerma and a computer generated index supplied with the CR system was investigated for two commercially available systems, one supplied by Fuji Medical Systems and the other by Kodak. The relationship between the index and incident air kerma could then be used as a substitute for optical density in monitoring AEC performance with respect to beam quality. It has been determined that an inverse linear relationship exists between the incident air kerma and the Sensitivity Number for the Fuji CR system and that a logarithmic relationship exists between the Exposure Index and incident air kerma for the Kodak CR system. In order to quantify these relationships further, the dependence of Sensitivity Number and Exposure Index on beam quality and incident kVp have been investigated. Using the results from the above investigations, acceptable limits for both Sensitivity Number and Exposure Index, can be established to test for correct AEC function, with respect to Beam Quality Dependence.

Survey of doses in screening mammography.

A survey was conducted over a period of several weeks to ascertain the mean glandular dose (MGD) to breast tissue arising from screening mammography. This survey found a MGD of 2.26 mGy per film for a sample of 2051 films and an average value of the MGD for each woman screened of 4.6 mGy for the 490 women included in the sample. The results revealed that there was a slight but significant trend towards lower MGD values with increasing age over 60. This study offers a method whereby from a knowledge of the X-ray tube potential, breast thickness and the recorded mAs a relatively reliable estimate of the MGD may be obtained for individual women.

Computed tomography pelvimetry: accuracy and radiation dose compared with conventional pelvimetry.

Several publications in the past few years have indicated that computed tomography (CT) pelvimetry is preferable to conventional pelvimetry when considering accuracy and radiation dose. Many of the previous publications have, however, compared state of the art CT pelvimetry with outmoded conventional pelvimetry techniques. This study compared both the accuracy and the radiation dose of CT pelvimetry with conventional pelvimetry as practised in two large teaching obstetric hospitals in Melbourne. The study did not demonstrate any significant difference in the accuracy between the two methods. The radiation dose to the fetal gonads was also similar. The radiation dose using CT pelvimetry could be significantly lowered if the axial CT section through the ischial spines were excluded from the CT technique.

The usefulness of K-edge filters in automatic brightness controlled fluoroscopy and digital subtraction angiography.

This paper presents the results of a study in which the efficacy of using high atomic number K-edge filters in place of non-selective filters, in Automatic Brightness Controlled fluoroscopy and Digital Subtraction Angiography was examined. Filters investigated in the study were copper, and aluminium [as examples of non-selective filters], gadolinium, erbium and tantalum. The results of this study would suggest, with the possible exception of gadolinium as an added filter in angiography of thin anatomical parts, that the selective K-edge filters offer no particular advantage over the non-selective filters from the viewpoint of either patient dose reduction or image contrast. Further, for imaging of all but the thinnest anatomical parts, their use adds substantially to the problems of x-ray tube loading.

Radiation absorbed dose calculations for samarium-153-EDTMP localized in bone.

Calculations have been undertaken to estimate the likely radiation dose received by patients undergoing treatment with samarium-153-EDTMP. Previously known bone structure parameters have been employed to partition correctly the energy absorbed in the bone matrix between red bone marrow, yellow marrow, and various types of mineral bone. Both uniform surface and volume distribution of the radioactivity are considered. The key findings of the calculations can be stated in terms of the MIRD "S-factors" for red bone marrow and the endosteal layer of cells on bone surfaces. In particular, the S-factor for red bone marrow is either 0.0276 mGy/MBq.h or 0.0077 mGy/MBq.h for surface and volume distributed radioactivity, respectively. For the endosteal layer of thickness (10 microns) on bone surfaces, the corresponding values are 0.0723 mGy/MBq.h and 0.0213 mGy/MBq.h, respectively.

A survey of doses to patients in a large public hospital resulting from common plain film radiographic procedures.

A semi-empirical method allowing ready calculation of skin absorbed doses has been applied in a survey of patients undergoing a number of common plain film radiographic procedures in a large public hospital. As an alternative indicator of risk, the quantity Mean Energy Imparted, has also been determined for some procedures. Survey results are compared with those obtained in a recent United Kingdom survey and against the most recent data available for Australia. In the special situation relating to mammography, the results are presented in terms of mean glandular doses.