Full-Field Digital Versus Screen- Film Mammography: Comparative Accuracy in Concurrent Screening Cohorts

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1 Accuracy of Mammography Women s Imaging Original Research WOMEN S IMAGING Marco Rosselli Del Turco 1 Paola Mantellini 1 Stefano Ciatto 1 Rita Bonardi 1 Francesca Martinelli 1 Barbara Lazzari 1 Nehmat Houssami 2 Rosselli Del Turco M, Mantellini P, Ciatto S, et al. Keywords: breast cancer, digital imaging, mammography, mammography screening, women s imaging DOI: /AJR Received March 23, 2007; accepted after revision May 18, Centro per lo Studio e la Prevenzione Oncologica, Viale A. Volta 171, Florence, Italy. Address correspondence to S. Ciatto (s.ciatto@cspo.it). 2 Screening and Test Evaluation Program, School of Public Health, University of Sydney, Sydney, Australia. AJR 2007; 189: X/07/ American Roentgen Ray Society Full-Field Digital Versus Screen- Film Mammography: Comparative Accuracy in Concurrent Screening Cohorts OBJECTIVE. The purpose of this study was to compare the diagnostic accuracy of digital mammography with that of screen-film mammography in concurrent cohorts participating in the same population-based screening program. MATERIALS AND METHODS. In a retrospective study covering , we compared digital with screen-film mammography in two concurrent screening cohorts of women years old participating in a screening program operated from mobile units. Each cohort had 14,385 participants matched by age and interpreting radiologist from all participants consecutively registered. We compared recall and cancer detection rates. RESULTS. The recall rate was higher for digital mammography (4.56% vs 3.96%, p =0.01), particularly when clustered microcalcifications were the only finding (1.05% vs 0.41%, p =10 6 ) and for younger women (50 59 vs years, 5.12% vs 4.17%, p = 0.009). The higher recall rate for digital mammography was mainly evident at incidence screening. The recall rate due to poor technical quality was lower with digital mammography (0.27% vs 0.50%, p = 0.002), possibly because real-time feedback was available. The detection rate was higher for digital mammography (0.72% vs 0.58%, p = 0.14), particularly for cancers depicted as clustered microcalcifications (0.26% vs 0.12%, p = 0.007), in younger (50 59 years) women (0.63% vs 0.42%, p = 0.09), and in denser breasts (1.09% vs 0.53%, p = 0.24). No significant difference was observed in positive predictive value on recall for digital mammography or screen-film mammography. Early cancer (ptis, pt1mic, pt1a) was more frequent in cancer detected with digital mammography than in that detected with screen-film mammography (41.3% vs 27.3%, p = 0.06). CONCLUSION. Digital mammography may be more effective than screen-film mammography in contemporary screening practice in mobile units. The data indicate that digital mammography depicts more tumors than does screen-film mammography, especially lesions seen as microcalcifications. The potential association with improved outcome warrants further study. espite considerable potential advantages (electronic archiving, D teleconsultation, telereporting, processing after image acquisition, immediate digital magnification, reduced radiation exposure, computer-assisted detection) and evidence of at least comparable accuracy, the uptake into screening practice of digital mammography instead of conventional screen-film mammography has been slow. This slow adoption may be due to the following factors: the need for dedicated systems (e.g., dedicated workstations that allow short review times, dedicated radiology information systems, and a PACS) for digital mammographic screening activity to reach the same efficiency parameters as screening with conventional screen-film techniques; the resistance of radiologists to accept lower spatial resolution, even though high contrast allows better diagnostic performance and physical measurements have shown that digital mammography performs better in visualization of very-low-contrast details and at least as well for high-contrast details, even when details smaller than pixel size are presented [1]; the higher purchase and maintenance costs of imaging equipment and the added requirements for digital archiving and display [2]; a lack of large-field detectors to accommodate large breasts. Studies showing the diagnostic accuracy of digital mammography to be comparable with that of screen-film mammography have often focused on symptomatic, diagnostic, and selfreferral settings [3 5]. In only a few studies [6 9] have investigators examined the accuracy of this technique in population-based screening 860 AJR:189, October 2007

2 Accuracy of Mammography practice. The multicenter Digital Mammographic Imaging Screening Trial [9] showed that digital mammography is more sensitive than screen-film mammography in some groups (women younger than 50 years, women with dense breasts, and premenopausal and perimenopausal women), although overall the two techniques have similar accuracy. There is, however, a paucity of evidence on the diagnostic accuracy of digital mammography as a reliable alternative to screen-film mammography in the context of contemporary screening implemented as part of an organized program. The screening program in the district of Florence, Italy, provides all population-based organized screening services in that region and operates four mobile mammography units equipped with digital and screen-film mammography. All image interpretation and screening assessments are conducted by the same radiologists at a single institution. The purpose of this retrospective study was to compare the diagnostic accuracy of digital mammography with that of screen-film mammography in concurrent screening cohorts participating in the same population-based organized screening program. Materials and Methods Test Methods We evaluated screening mammograms obtained from January 2004 to October 2005 in two mobile units of the Florence, Italy, screening program. Since 2001, one mobile service had been equipped with a digital mammography unit (2000D, GE Healthcare) and the other with a screen-film unit (Mammomat 1000, Siemens Medical Solutions). The two machines had comparable relevant technical parameters (focal spot size, grid). The digital mobile unit was connected to the main center by a wireless +2 Mbit/s high-bit-rate digital subscriber line connection. Digital images were automatically sent to a dedicated diagnostic workstation (MammoReport, Siemens Medical Solutions) for mammographic screening. The unit had a 9-megapixel image size, which allowed standard image processing (e.g., magnification, zoom, image inversion), and high-brightness, high-resolution, flat-panel monitors (Coronis 5MP, Barco). The workstation accommodated scheduling of several examinations, viewing of images with those from previous screening examinations if available, and double review. The images were also stored in an electronic archive (Radstore, GE Healthcare). To avoid loss of files due to transmission failure, backup copies of the images were saved on the CD-ROM of the mobile unit before transmission. Both the screen-film and digital mammography systems were subjected to a quality control program according to the European guidelines for quality assurance in mammographic screening, including an addendum on digital mammography [10]. To select the appropriate working point according to the aslow-as-reasonably-achievable principle for the digital mammography system, complete physical characterization was performed [10]. For digital mammography, the entrance surface exposure for a standard breast under clinical conditions was 7.1 mgy, resulting in a 1.8-mGy average glandular dose; for screen-film mammography, the exposure was 7.5 mgy, resulting in an average glandular dose of 1.6 mgy. The diagnostic workstation monitors were subjected to a regular quality control program according to the American Association of Physicists in Medicine Task Group 18 report Assessment of Display Performance for Medical Imaging Systems [11]. No special image processing was adopted for soft-copy review. Radiologists could modify image brightness and contrast and could use magnification of black and white inversion, but the use of such features was not recorded. Digital and screen-film mammograms in the study were interpreted by four radiologists, each with more than 5 years of experience in mammographic screening and an average workload of more than 10,000 mammograms interpreted per year. Screen-film mammograms were developed in a separate session at the central unit of our institution. Interpretation was not immediate for either screenfilm or digital mammography. At the time of imaging in the mobile unit, no real-time feedback (e.g., to repeat imaging in case of inadequate positioning) was provided to the radiographer for screen-film mammography, but feedback was possible for digital mammography because the digital image obtained was displayed on the monitor. Double review was performed and was not independent, the second reviewer being aware of the first reviewer s report. Thus, recall for further assessment was based on suspicion by either reviewer. At incidence screening, previous mammograms (digital or screen film) were available for comparison at the request of either radiologist. Computer-assisted detection was not used for digital or screen-film mammography because it was not standard practice in most European screening programs. No special protocol existed regarding the use of digital or screen-film mammography units in different quarters of the city. Women who underwent previous mammography in the digital mammography mobile unit did not automatically undergo follow-up mammography in the digital unit. Participants Population-based screening has been ongoing since 1970 in the district of Florence. The main features of the program have been reported [12]. The efficacy of the program was shown in a case control study [13]. Screening is offered to all women years old. The cancer detection rate at prevalence screening is 8.25 cases per 1,000 and at incidence screening is 3.45 cases per 1,000 [12]. Data from the local cancer registry [14] indicate that the two areas served by the mobile screening units in this study had similar breast cancer incidence and detection rates at previous rounds of screen-film mammography. The detection rates at screening in 2003 were 5.90 cases per 1,000 in the screen-film mammography study area and 5.49 cases per 1,000 in the digital mammography study area. To ensure that concurrent cohorts were comparable, subjects were included from all participants screened for the study duration after matching by decade of life and each possible pair of reviewing radiologists (Fig. 1). All images were interpreted under the same review and evaluation protocols. Statistical Analysis and Methods The following data were recorded for each participant: age group (50 59 or years), screening round (first or repeated), reviewing radiologist, mammographic density categorized as percentage volume occupied by fibroglandular density (< 25%, BI-RADS fatty; 25 75%, BI-RADS scattered fibroglandular and heterogeneously dense; > 75%, BI- RADS extremely dense), screening test outcome (normal, referral, recall for assessment), reason for recall (subjective symptoms other than pain alone, usually < 1% of screening participants, excluded from present study evaluation; radiologic abnormality worth further investigation; poor technical quality of imaging or positioning), type of radiologic abnormality prompting recall (clustered microcalcifications the only finding, mass, architectural distortion [we ignored associated findings to allow simpler statistics]), and final outcome of diagnostic assessment (normal finding, benign lesion, cancer). Final outcome of screen-positive cases suspicious at diagnostic assessment, including core biopsy, and referred for surgical management was defined according to surgical histologic findings. The accuracy of digital mammography was compared with that of screen-film mammography for recall, cancer detection rate, and positive predictive value at recall in the overall series and according to variables such as age, breast density, prevalence (first) or incidence (subsequent) screening round, and type of radiologic abnormalities. Because our data showed definite differences in the two mammographic methods for cancers depicted as clustered microcalcifications, we extended the evaluation by reviewing all participants recalled on the basis of the presence of microcalcifications. Two radiologists with long-standing experience in screening mammography reviewed all AJR:189, October

3 Screened subjects January 2004 October 2005: 36,262 Assessment finding benign: 541 (3.8%) Surgical finding benign: 12 (0.08%) Fig. 1 Flow diagram of study. Normal screen result: 13,728 (95.4%) Matched: 14,385 (100.0%) such cases independently and used consensus in case of disagreement. These radiologists classified the cases according to mammographic morphologic features and level of suspicion. An alternative system for reporting findings on breast imaging was based on a standardized categoric scale (1, negative; 2, benign; 3, equivocal; 4, suspicious; 5, malignant) with published estimates of the likelihood of malignancy [15, 16]. The assessment categories, referred to as R1 R5, were only partially consistent with BI-RADS. The R3 category in our practice prompts assessment rather than early recall; the latter is not a recommended option in screening protocols at our center or in European standards [10]. Statistical significance of observed differences in recall and cancer detection rates was determined by univariate analysis with the chisquare test (Stata 8.0 SE software, StataCorp). The significance level was set at p < Results Overall 28,770 mammograms (14,385 with each technique) (Fig. 1) were included in the evaluation. Excluded before matching by age and reporting radiologist were 135 subjects who underwent mammography for assessment of symptoms. Screened in digital mammography unit: 14,706 Recalled to assessment: 657 (4.6%) Assessment finding abnormal: 116 (0.8%) Surgical finding malignant: 104 (0.7%) Matching according to age and reporting radiologist Eligible for inclusion in analysis: 28,770 Screened in screen-film mammography unit: 21,556 Recalled to assessment: 570 (4.0%) Assessment finding abnormal: 93 (0.6%) Surgical finding malignant: 84 (0.6%) Matched: 14,385 (100.0%) Normal screen result: 13,815 (96.0%) Assessment finding benign: 477 (3.3%) Surgical finding benign: 9 (0.06%) TABLE 1: Distribution of Radiologic Breast Density, Age, and Screening Round (n = 14,385) (n = 14,385) Mammographic density (%) ,757 (33.0) 5,024 (34.9) ,886 (61.7) 8,722 (60.6) > (5.1) 639 (4.4) ,755 (46.9) 6,755 (46.9) ,630 (53.0) 7,630 (53.0) Prevalence 1,705 (11.8) 1,751 (12.1) Incidence 12,680 (88.1) 12,634 (87.8) Note Values in parentheses are percentages. Participants Table 1 shows the distribution of radiologic breast density, age group, and screening round for the two mammographic techniques. The results show the two cohorts were generally comparable. Recall Rate Table 2 shows that the overall recall rate, including recall because of poor technical quality, differed significantly between screenfilm mammography (3.96%) and digital mammography (4.56%) (χ 2 df =1= 6.44, p = 0.01). Relative to screen-film mammography, digital mammography was associated with significantly more recalls because of radiologic abnormality (4.29% vs 3.46%, χ 2 df =1 = 13.42, p = ) and with significantly less recall because of poor technical quality (0.27% vs 0.50%, χ 2 df =1 = 9.84, p = 0.002). Digital mammography had a sig- 862 AJR:189, October 2007

4 Accuracy of Mammography TABLE 2: Recall Rate (n = 14,385) nificantly higher recall rate because of microcalcifications than did screen-film mammography (1.05% vs 0.41%, χ 2 df =1 = 39.53, p =10 6 ), but the recall rates did not differ for masses (screen-film mammography, 2.85%; digital mammography, 3.07%; χ 2 df =1 = 1.23; p = 0.25) or distortions (screen-film mammography, 0.19%; digital mammography, 0.16%; χ 2 df =1 = 0.17; p = 0.57). Among women years old, the recall rate was significantly higher for digital mammography than for screen-film mammography (5.12% vs 4.17%, χ 2 df =1= 6.84, p = 0.009). Recall rates were higher for digital mammography in all breast density categories, but the only significant difference was recorded for very dense (> 75%) breasts (4.85% vs 2.69%, χ 2 df =1 = 4.48, p = 0.03). Recall rates were similar for screen-film and digital mammography at prevalence screening, but a significantly higher recall rate was observed for digital mammography (4.15% vs 3.44%, χ 2 df =1= 8.70, p = 0.003) at incidence screening. Cancer Detection Rate There were 188 cancers detected (84 in the screen-film mammography group, 104 in the digital mammography group), and 21 benign lesions were subjected to surgical biopsy (nine in the screen-film mammography group, 12 in the digital mammography group). There were 144 invasive cancers (69 in the screen-film mammography, 75 in the digital mammography group), and 44 malignant tumors were ductal carcinoma in situ (DCIS) (15 in the screen-film mammography group, 29 in the digital mammography group). Thus, overall, 23.4% (44/188) of all malignant tumors detected in this study were DCIS. The TNM pt category at diagnosis in the screen-film mammography series was ptis in 15 cases, pt1mic in one case, pt1a in seven cases, pt1b in 24, pt1c in 26, pt2 in seven, pt4b in two, and ptx in two cases. The corresponding distribution for the digital mammography series was ptis in 29 cases, pt1mic in five, pt1a in nine, pt1b in 17, pt1c in 38, pt2 in five cases, and ptx in one case. The frequency of early-stage lesions (ptis, pt1mic, pt1a) was higher in the digital than in the screen-film mammography series (41.3% vs 27.3%, χ 2 df = 1 = 3.38, p = 0.06). Table 3 shows the cancer detection rate for the screen-film and digital mammography groups according to type of abnormality on mammography, age group, breast density category, and screening round. The most notable finding was that significantly more cases of cancer depicted as microcalcifications were detected on digital mammography than on No. Recalled Recall Rate (%) a No. Recalled Recall Rate (%) a Reason for recall Radiologic abnormality Poor technical quality Type of abnormality on mammogram Mass Distortion Clustered microcalcifications (n = 6,755) (n = 7,630) Density (%) 0 25 (n = 4,757 screen film; n = 5,024 digital) (n = 8,886 screen film; n = 8,722 digital) > 75 (n = 742 screen film; n = 639 digital) Prevalence (first) (n = 1,705 screen film; n = 1,751 digital) Incidence (repeated) (n = 12,680 screen film; n = 12, digital) Total (n = 14,385) a Percentage of screened subjects. screen-film mammography (0.26% vs 0.12%, χ 2 df = 1 =7.15, p = 0.007). In addition, digital mammography had a higher detection rate than screen-film mammography among women years old and a higher overall detection rate than screen-film mammography at incidence screening. The differences between the two mammographic methods, however, did not reach statistical significance. The main characteristics of tumors (invasive or DCIS) depicted as clustered microcalcifications and detected on screen-film and digital mammography are reported in Table 4. Positive Predictive Value for Recall The recall rate for digital mammography was higher than for screen-film mammography, but this rate was compensated by the additional cases of cancers detected. The positive predictive value for finding cancer among recalled cases was 15.9% for digital mammography and 14.7% for screen-film mammography (p = 0.65). Corresponding values for other study variables are reported in Table 5, but minor observed differences did not reach statistical significance. Discussion This comparative study was based on two large concurrent series of screening participants p AJR:189, October

5 TABLE 3: Cancer Detection Rate (n = 14,385) Cancer Detection Cancer Detection No. Detected Rate (%) a No. Detected Rate (%) a p Mass Distortion Clustered microcalcifications (n = 6,755) (n = 7,630) Density (%) 0 25 (n = 4,757 screen film; n = 5,024 digital) (n = 8,886 screen film; n = 8,722 digital) > 75 (n = 742 screen film; n = 639 digital) Prevalence (first) (n = 1,705 screen film; n = 1,751 digital) Incidence (repeated) (n = 12,680 screen film; n = 12, digital) Total (n = 14,385) a Percentage of screened subjects. TABLE 4: Histologic Grade and Mammographic Characteristics of Malignant Tumors Depicted as Clustered Microcalcifications as the Only Finding Characteristic No. of Tumors No. of Cases of DCIS No. of Tumors No. of Cases of DCIS Histologic grade I II III NA Degree of suspicion R R R NA 1 0 Morphologic feature Granular Linear or branching NA 1 0 Total Note DCIS = ductal carcinoma in situ, NA = not available. drawn from the same population within a single screening program. The two groups of participants had similar composition as to age, breast density, and screening round (first or repeated). The mammograms were interpreted by the same radiologists during the same period and according to the same protocol. The main difference between the two series was the mammographic technique. We believe that differences in recall and cancer detection rates can be reasonably attributed to mammographic method. Both cancer detection rates and recall rates in our study were in line with standards for population screening, and more cases of cancer were detected with digital than with screen-film mammography. This finding is concordant with the work of other investigators [8, 9]. As expected, the overall need for recall was associ- ated with age and breast density, most likely a result of greater radiologic uncertainty in the presence of denser breasts, possibly in combination with a residual proportion of first-round (prevalence screen) examinations (lack of previous results for comparison) in the 50- to 59- year age range. The higher recall rate for digital mammography was evident at incidence but not at prevalence screening. We have no explanation for this finding, except for the limited sample size ( 10% of each compared cohort) in the latter group. Overall, digital mammography had a higher recall rate than screen-film mammography but had a higher cancer detection rate, although the difference did not reach statistical significance. Digital mammography was associated with significantly less need for recall because of poor technical quality than was screen-film mammography. It is worth emphasizing that this study was based on mammography performed in mobile units. Developing of screen-film mammograms was deferred, so radiographers could not immediately check proper exposure and positioning. These factors were checked for digital mammography, however, because the digital images were immediately displayed on the monitor in the mobile unit. Although we cannot exclude the possibility that better imaging quality and the opportunity for postprocessing with digital mammography may have contributed to the lower recall rate, lack of immediate image feedback may explain, at least in part, the 864 AJR:189, October 2007

6 Accuracy of Mammography TABLE 5: Positive Predictive Value for Detection of Cancer (n = 14,385) Positive Predictive Positive Predictive No. Value (%) a No. Value (%) a p Mass 63/ / Distortion 3/ / Clustered microcalcifications 18/ / (n = 6,755) 29/ / (n = 7,630) 55/ / Density (%) 0 25 (n = 4,757 screen film; n = 5,024 digital) 15/ / (n = 8,886 screen film; n = 8,722 digital) 65/ / > 75 (n = 742 screen film; n = 639 digital) 4/ / Prevalence (first) (n = 1,705 screen film; n = 1,751 digital) 14/ / Incidence (repeated) (n = 12,680 screen film; n = 12,634 70/ / digital) Total 84/ / a Percentage of subjects recalled. higher recall rate for screen-film mammography. The findings on this issue may provide incentive for mobile mammography programs to convert to digital systems. The higher detection rate with digital mammography was more evident among younger women and women with denser breasts, both conditions being traditionally associated with lower sensitivity of screen-film mammography, further confirming the findings reported by other authors [9] for such subgroups. The lack of statistical significance in our data might have been due to sample size. Digital mammography had a significantly higher detection rate than screen-film mammography for clustered microcalcifications, which caused both the recall and cancer detection rates to be significantly higher for lesions with this feature. Traditional thought has been that calcifications are best detected with higher spatial resolution, which is conventionally lower with digital mammography than with screen-film mammography. It may well be that the compensatory conditions of increased contrast resolution in digital mammography allow enhanced visibility of calcifications. Whether the increased rate of detection of cancers depicted as clustered microcalcifications translates into a greater screening efficacy can be questioned. Cancers associated with this radiologic pattern likely may be more indolent cases, and their detection may not affect mortality [17]. We acknowledge this possibility, more so because microcalcifications detected on digital mammograms in our study were more frequently DCIS, were of lower to intermediate histologic grade, and had a less suspicious morphologic pattern (BI-RADS 3 vs 4 5, or granular vs linear branching). Our findings on this issue differ slightly from those of the Digital Mammographic Imaging Screening Trial [9], in which more cases of high-grade DCIS were detected with digital mammography. Although we have no explanation for such a difference, it should be taken into consideration that DCIS represented almost 31% of the cases of cancer in the Digital Mammographic Imaging Screening Trial and less than 25% of cases of cancer in our series. The digital mammography series in our study had a higher borderline significant frequency of early-stage cancers (ptis, pt1mic, pt1a) than did the screen-film mammography series. This finding suggests a higher sensitivity of digital mammography than of screen-film mammography for more subtle lesions. It also explains in part why digital mammography did not have an advantage at prevalence screening, at which cancers are less likely to have subtle features relative to incidence screening. These findings warrant further study with larger series of images to determine whether digital mammography does lead to detection of cancers with a more favorable stage distribution. One possible limitation of our study was that we found a better detection rate with one screening test relative to another, yet this finding cannot on its own be assumed to translate into screening benefit [17]. Neither this study nor other studies of digital mammography for screening were designed to measure mortality as an end point. However, assessing differences in interval cancer rates after sufficient follow-up will provide an indication of expected screening benefit [17]. A study monitoring interval cancers in the two concurrent series used in this study is ongoing. Another possible limitation was that the matching used in the study design caused subject losses. However, we retained approximately 80% of all consecutive screening participants in the analysis. Most of the nonselected cases were from the screen-film mammography series, but this factor should not account for potential selection bias due to matching characteristics. This study showed that digital mammography is at least as accurate and effective as screen-film mammography in current screening practice. Our data show that digital mammography leads to additional cancer detection in population screening. In accordance with the few existing studies of digital mammography in screening, our results show a greater detection rate, despite a higher recall rate, for digital mammography than for screen-film mammography and suggest that digital mam- AJR:189, October

7 mography is more sensitive among younger women and women with denser breasts. The higher cancer detection rate for digital mammography is associated with cancers depicted as clustered microcalcifications and possibly cancers with a more favorable stage distribution. Although these findings can be expected to translate into an important screening benefit, future comparison of interval cancer rates [18] may indicate whether these aspects of digital mammography are likely to have an impact on breast cancer mortality. Acknowledgments We are grateful to Daniela Ambrogetti, Donata Tanzini, Patrizia Falini, Elisabetta Gentile, Miriam Gabrielleschi, Lidia Pes, Verusca Giotti, and Antonello Casini for their invaluable contribution to data collection and for their support in the implementation of digital mammography in the screening program. References 1. Thijssen M, Veldkamp W, van Engen R, Swinkels M, Karssemeijer N, Hendriks J. Comparison of the detectability of small details in a film-screen and a digital mammography system by the imaging of a new CDMAN-Phantom. In: Yaffe MJ, ed. Digital mammography IDDM 2000: 5th International Workshop on. Madison, WI: Medical Physics, 2001: Ciatto S, Brancato B, Baglioni R, Turci M. A methodology to evaluate differential costs of full field digital as compared to conventional screen film mammography in a clinical setting. Eur J Radiol 2006; 57: Di Nubila B, Cassano E, Origgi D, et al. Analogic versus digital mammographic examination a radiological study of mammary microcalcifications on 52 surgical samples [in English and Italian]. Radiol Med (Torino) 2003; 106: Lewin JM, D Orsi CJ, Hendrick RE, et al. Clinical comparison of full-field digital mammography and screen-film mammography for detection of breast cancer. AJR 2002; 179: Bonardi R, Ambrogetti D, Ciatto S, et al. Conventional versus digital mammography in the analysis of screen-detected lesions with low positive predictive value. Eur J Radiol 2005; 55: Skaane P, Young K, Skjennald A. Population-based mammography screening: comparison of screenfilm and full-field digital mammography with softcopy reading Oslo I Study. Radiology 2003; 229: Skaane P, Skjennald A. Screen-film mammography versus full-field digital mammography with softcopy reading: randomized trial in a populationbased screening program the Oslo II Study. Radiology 2004; 232: Irwig L, Houssami N, van Vliet C. New technologies in screening for breast cancer: a systematic review of their accuracy. Br J Cancer 2004; 90: Pisano ED, Gatsonis C, Hendrick E, et al. Diagnostic performance of digital versus film mammography for breast-cancer screening. N Engl J Med 2005; 353: [erratum in N Engl J Med 2006; 355:1840] 10. Perry N, Broeders M, de Wolf C, Tornberg S, Holland R, von Karsa L, eds. European guidelines for quality assurance in breast cancer screening and diagnosis, 4th ed. Luxembourg, Luxembourg: European Communities, American Association of Physicists in Medicine Task Group 18 Imaging Informatics Subcommittee. Assessment of display performance for medical imaging systems. OR_03.pdf. AAPM online report no. 03. Published April Accessed July 21, Zappa M, Falini P, Bonardi R, et al. Monitoring interval cancers in mammographic screening: the Florence District programme experience. Breast, 2002; 11: Palli D, Del Turco MR, Buiatti E, et al. A case-control study of the efficacy of a non-randomized breast cancer screening program in Florence (Italy). Int J Cancer 1986; 38: Paci E, Crocetti E, Miccinesi G, et al. Tuscany Cancer Registry. In: Parkin DM, Whelan SL, Ferlay J, Teppo L, Thomas DB, eds. Cancer incidence in five continents, vol. VIII. Lyon, France: IARC Scientific Publications, 2002: Houssami N, Irwig L. Likelihood ratios for clinical examination, mammography, ultrasound and fine needle biopsy in women with breast problems. Breast 1998; 7: Houssami N, Irwig L, Simpson JM, McKessar M, Blome S, Noakes J. Sydney Breast Imaging Accuracy Study: comparative sensitivity and specificity of mammography and sonography in young women with symptoms. AJR 2003; 180: Irwig L, Houssami N, Glasziou P, Armstrong B. How should we evaluate new screening tests for breast cancer? BMJ 2006; 332: Ciatto S, Rosselli Del Turco M, Zappa M. The detectability of breast cancer by screening mammography. Br J Cancer 1995; 71: AJR:189, October 2007