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

Abstract

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 ).

How many physicists does it take to test a mammography unit?

“…Once again, RANZCR [13] and ACPSEM [14] must be acknowledged for the swift development of routine QC guidelines for digital mammography. Furthermore, ACPSEM, with funding from the Australian Department of Health developed an online, interactive training program for radiographers working in digital mammography which aimed to provide a nationally consistent approach to QC training and processes.…”

“…Furthermore, my own testing experience indicates that the sensitivity of CR plates degrades over time and for CR systems greater than 3 years old, the MGD necessary to meet SDNR and image quality requirements is about 20% higher than that for a new system. In 2012, the ACPSEM therefore recommended that only DR technology should be approved for future purchases of equipment for screening mammography in Australia and New Zealand and existing CR systems should be progressively replaced [14].…”

A comparison of digital mammography detectors and emerging technology

“…The effective detector element (del) size is typically 50 mm and spatial resolution of 10 lp/mm is theoretically possible. 24 With indirect conversion detectors, X-rays are first converted to light photons in a scintillation layer (usually Caesium Iodide). Light photons are then converted to an electronic charge signal using a flat panel of amorphous silicon (a-Si) that incorporates an array of photodiodes.…”

“…The effective del size is typically 100 mm, corresponding to a maximum achievable spatial resolution of 5 lp/mm. 24 Direct conversion flat panel detectors utilise a semiconductor material known as amorphous selenium (a-Se) to convert X-rays directly to electronic charge. Nominal del sizes are 50e85 mm, which equates to a limiting spatial resolution of 6e10 lp/mm.…”

“…X-ray photons are then converted directly to electronic signal in a crystal silicon detector. 24 Since the publication of the Digital Mammography Imaging Screening Trial (DMIST) 10 ten years ago, research has shifted from a comparison of DM with screen-film, to the variation in performance of different digital detector technologies. Recently published studies have compared cancer detection rates, 16,21,22,25e27 patient dose 4e7,28 and image quality.…”