The United Kingdom, European and IAEA protocols for breast dosimetry in mammography make use of s-factors which allow for the use of different target/filter combinations. To supplement the existing protocols, a Monte Carlo computer program has been used to calculate s-factors for mammography using a tungsten target with silver filters of thicknesses 50-75 microm and for the same target filtered with 0.5 mm aluminium. The dosimetry protocols use slabs of polymethyl methacrylate (PMMA) of specified thicknesses to simulate the exposure of typical breasts. The equivalent thickness of PMMA has been calculated using a simplified approach for a wider range of x-ray spectra and for breast thicknesses of 2-11 cm. The results show that for the tungsten/silver target/filter combination, a single s-factor of 1.042 can be used with the protocols, but when the tungsten target is filtered with 0.5 mm of aluminium, it is necessary to select from a tabulation of s-factors against breast thickness. The equivalent thicknesses of PMMA for a given breast thickness show some dependence on beam quality and the values obtained differ from those presently used in the dosimetry protocols by an amount which depends upon breast thickness and half value layer (HVL). For the extreme case of an 11 cm breast and an HVL of 0.62 mm Al, the use of the protocol thickness would give rise to an error of 10%, but for breast thicknesses of 6 cm or less, the error is typically 2-3%.
A formalism is proposed for the estimation of mean glandular dose for breast tomosynthesis, which is a simple extension of the UK, European and IAEA protocols for dosimetry in conventional projection mammography. The formalism introduces t-factors for the calculation of breast dose from a single projection and T-factors for a complete exposure series. Monte Carlo calculations of t-factors have been made for an imaging geometry with full-field irradiation of the breast for a wide range of x-ray spectra, breast sizes and glandularities. The t-factors show little dependence on breast glandularity and tables are provided as a function of projection angle and breast thickness, which may be used for all x-ray spectra simulated. The T-factors for this geometry depend upon the choice of projection angles and weights per projection, but various example calculations gave values in the range 0.93-1.00. T-factors are also provided for the Sectra tomosynthesis system, which employs a scanned narrow-beam imaging geometry. In this quite different configuration, the factor (denoted T(S)) shows an important dependence on breast thickness, varying between 0.98 and 0.76 for 20 and 110 mm thick breasts, respectively. Additional data are given to extend the current tabulations of g-, c- and s-factors used for dosimetry of conventional 2D mammography.
ObjectiveContrast-enhanced spectral mammography (CESM) examination results in a low-energy (LE) and contrast-enhanced image. The LE appears similar to a full-field digital mammogram (FFDM). Our aim was to evaluate LE CESM image quality by comparing it to FFDM using criteria defined by the European Reference Organization for Quality Assured Breast Screening and Diagnostic Services (EUREF).MethodsA total of 147 cases with both FFDM and LE images were independently scored by two experienced radiologists using these (20) EUREF criteria. Contrast detail measurements were performed using a dedicated phantom. Differences in image quality scores, average glandular dose, and contrast detail measurements between LE and FFDM were tested for statistical significance.ResultsNo significant differences in image quality scores were observed between LE and FFDM images for 17 out of 20 criteria. LE scored significantly lower on one criterion regarding the sharpness of the pectoral muscle (p < 0.001), and significantly better on two criteria on the visualization of micro-calcifications (p = 0.02 and p = 0.034). Dose and contrast detail measurements did not reveal any physical explanation for these observed differences.ConclusionsLow-energy CESM images are non-inferior to FFDM images. From this perspective FFDM can be omitted in patients with an indication for CESM.Key Points• Low-energy CESM images are non-inferior to FFDM images.• Micro-calcifications are significantly more visible on LE CESM than on FFDM.• There is no physical explanation for this improved visibility of micro-calcifications.• There is no need for an extra FFDM when CESM is indicated.
Objectives:To investigate the referral pattern after the transition to full-field digital mammography (FFDM) in a population-based breast cancer screening programme.Methods:Preceding the nationwide digitalisation of the Dutch screening programme, an FFDM feasibility study was conducted. Detection and referral rates for FFDM and screen-film mammography (SFM) were compared for first and subsequent screens. Furthermore, radiological characteristics of referrals in digital screening were assessed.Results:A total of 312,414 screening mammograms were performed (43,913 digital and 268,501 conventional), with 4,473 consecutive referrals (966 following FFDM). Initially the FFDM referral rate peaked, and many false-positive results were noted as a consequence of pseudolesions and increased detection of (benign) microcalcifications. A higher overall referral rate was observed in FFDM screening in both first and subsequent examinations (p < .001), with a significant increase in cancer detection (p = .010).Conclusion:As a result of initial inexperience with digital screening images implementing FFDM in a population-based breast cancer screening programme may lead to a strong, but temporary increase in referral. Dedicated training in digital screening for radiographers and screening radiologists is therefore recommended. Referral rates decrease and stabilise (learning curve effect) at a higher level than in conventional screening, yet with significantly enhanced cancer detection.
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