David Cohen, M.D.·Published 11 June 2008·11 min read
Key points
The usefulness of mammography is dependent on the proper use of dedicated mammography equipment, the diagnostic skills of the interpreter, and assessing and diminishing barriers to its regular use.
Smith: Cancer Screening, Department of Cancer Control, American Cancer Society, Atlanta, Georgia C.
As knowledge and use of mammography slowly increased after the beginning of early promotion efforts, the Nationwide Evaluation of X-Ray Trends demonstrated a great variation in dose and image quality among mammography sites.
Troubled by the Nationwide Evaluation of X-Ray Trends report and hoping to alleviate the problems it identified, the ACS approached the ACR to stimulate the development of quality standards for mammography facilities.
The usefulness of mammography is dependent on the proper use of dedicated mammography equipment, the diagnostic skills of the interpreter, and assessing and diminishing barriers to its regular use. These issues have been and are currently being addressed in an effort to promote safe and effective mass screening for early-stage breast cancer.
As knowledge and use of mammography slowly increased after the beginning of early promotion efforts, the Nationwide Evaluation of X-Ray Trends demonstrated a great variation in dose and image quality among mammography sites. This report emerged at the time that the ACS was initiating its National Breast Cancer Awareness Screening Program.
Troubled by the Nationwide Evaluation of X-Ray Trends report and hoping to alleviate the problems it identified, the ACS approached the ACR to stimulate the development of quality standards for mammography facilities. With funding from the ACS, the voluntary ACR Mammography Accreditation Program was established and began to accredit mammography facilities in August 1987. The application process included a questionnaire to obtain information about personnel, volume, and type of examinations performed; the imaging system through evaluation of phantom images and dose delivery; and, most important, assessment of clinical images to evaluate positioning, contrast, compression, and image-label identifiers.
The process of clinical image evaluation was performed by a group of radiologists with extensive experience in mammography who were trained to identify problems in clinical images that would hinder or prevent identification of early breast cancer. Evaluation of the image processing was later added when it was learned that many problems identified by clinical image review could be traced to faulty processor performance. Over time, greater understanding of the link between high-quality mammography and the goals of breast cancer screening led to new regulatory initiatives.
Maryland was the first state to pass legislation pertaining to quality assurance in mammography. In 1986, legislation was passed that required mammography examinations to be performed with machinery designed and built only for mammography. These dedicated units were vastly superior to mammography performed on general purpose machines in terms of dose and image quality. By 1993, 41 states and the District of Columbia had either passed legislation or established regulations addressing quality mammography.
Toward the end of 1990, Congress added mammography to the benefit package for Medicare-eligible women and included quality standards for sites approved to provide services to Medicare beneficiaries. These standards were heavily influenced by the ACR Mammography Accreditation Program standards. Also in that year, Congress passed the Breast and Cervical Cancer Mortality Prevention Act of 1990 (PL 101-354), appropriating funds to the CDC for state programs to provide breast and cervical cancer screening to low-income women. Recognizing the importance of high-quality mammography, the CDC required facilities that provided services under this program to be certified by the Health Insurance Financing Administration and to have ACR accreditation. By this time, a mammography facility could have been operating under a state standard, a federal standard, and a voluntary standard, each of which could vary on important criteria related to quality.
Written and revised by
David Cohen, M.D.
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On the other hand, a facility might have operated with little or no oversight, because ACR accreditation was voluntary, and the facility might choose not to offer screening to Medicare beneficiaries or to participate in the CDC program. Although a majority of states had regulations governing mammography quality assurance, state oversight was inconsistent at best. Thus, even with the emergence of new quality-oriented programs, the majority of facilities still had uneven adherence to quality standards. In order to ensure that women could depend on a uniform set of quality standards in all mammography facilities, in 1992 Congress passed the Mammography Quality Standards Act (MQSA), which was signed by President George Bush in October of that year. Under MQSA, all facilities offering mammography services would be required to be accredited by a private accrediting body, undergo an annual on-site inspection, and be certified by an agency designated by the Secretary of Health and Human Services. {pagebreak}
The following year, the Food and Drug Administration was assigned the task of enforcing MQSA by establishing standards, regulations, inspection processes, compliant mechanisms, and penalties for failure to comply with the regulations.
At approximately the same time as MQSA was being enacted, the AHCPR convened a panel to produce clinical practice guidelines on the quality determinants of mammography for interpreting physicians, clinicians, and consumers. The panel considered the entire process involved in providing quality mammography to consumers, including (a) actions before the examination related to scheduling, including triaging patients into screening or diagnostic examinations; (b) appropriate data to collect for the patient's history; (c) the role of the imaging team, including qualifications; (d) machinery standards, dose limitations, quality control procedures, and the importance of routine evaluation of clinical images and the imaging system; and (e) the communication of results to patients.
The development of these clinical practice guidelines underscores the importance of factors beyond image quality that contribute to a high-quality examination. Among the most important of these factors is communication with patients and referring physicians.
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Many studies have demonstrated that clinicians often fail to communicate mammography results to patients. In part, this pattern has been influenced by a tradition of "no news is good news," but there also is evidence of a failure to communicate abnormal findings. The panel strongly recommended that all women, regardless of whether their mammograms were negative, be informed by the imaging facility of their results. The preferred route suggested was use of a series of standardized letters that stressed subsequent steps, if any, to be taken by the woman, but the panel strongly urged that the method of communication should be tailored to the results of the examination.
For example, the panel firmly discouraged notification of abnormal results initially by mail. Because the advocacy community regarded direct reporting as an important factor in the overall quality assurance of an examination, the requirement for direct reporting was included in the 1998 reauthorization of the MQSA.
In addition to determinants of a high-quality examination, the AHCPR panel addressed the critical issue of assessing outcome data from mammography facilities by use of medical audits. Data (both collected and derived) required for the basic medical audit include (a) the number and type of mammography examinations performed; (b) the recall rate from screening mammography for further evaluation; (c) the PPV of screening mammography, as well as the PPV of patients sent to biopsy for a mammographic abnormality; and (d) the stage of disease at diagnosis and the breast cancer detection rate per 1,000 women screened. A more advanced audit requires linkage to a breast cancer registry, which is not possible in most areas in the United States. {pagebreak}
Here, one would also evaluate the sensitivity and specificity of screening mammography. The document also established goals for many of these outcome parameters as a guideline for facilities, noting, however, that outcome data vary based on the size of the practice or number of audits in the database and by the underlying characteristics of the population being screened. Although a more complete review of the document is not within the scope of this chapter, the interested reader is urged to review this set of guidelines.
The final and arguably most critical step toward quality mammography is interpretation. A major barrier toward this educational goal had been the absence of any standardized language for mammographic features. Through the efforts of the ACR, with support from various clinical colleges, including the American College of Surgeons (ACS) and the American College of Obstetrics and Gynecology, a multidisciplinary committee was established in the early 1990s to address the suboptimal and often confusing terminology used in mammography reports. The document produced by this committee is the Breast Imaging Reporting and Data System (BI-RADS). BI-RADS is designed to standardize mammographic reporting, reduce confusion in breast imaging interpretations, and facilitate outcome monitoring. The system is divided into four sections:
Breast imaging lexicon. An illustrated review of all the findings seen on a mammogram with suggested terminology as well as guidance regarding whether the findings are worrisome for malignancy, are probably benign, or are definitely benign.
Reporting system. Provides an organized approach to image interpretation and reporting. Several sample reports are included to illustrate the suggested format for different mammographic scenarios.
Follow-up outcome monitoring. Describes minimum data to be collected and used to calculate important audit measures, allowing each radiologist to assess his or her overall performance in mammography interpretation.
ACR National Mammography Database. A preliminary effort for collection of national data that will ultimately allow groups to adjust their thresholds by comparison with pooled national data.
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There are six categories in BI-RADS that cover all possible initial and summary interpretations. Category 0 is "assessment is incomplete." This category should be used on reports of screening mammograms that require further evaluation. After this evaluation is complete or in the case of screening examinations that do not require assessment, there are five final categories. Category 1 is a "negative" examination. It does not require comment, and the patient is encouraged to return for routine screening in 1 year. Category 2 is a "benign finding." This is also a negative examination, but the interpreting physician may wish to describe a benign feature for subsequent reviewers. The patient is encouraged to return for routine screening in 1 year. Category 3 is for a "probably benign finding." This category is reserved for findings that have an extremely low probability of malignancy (i.e., 2% or less). It is not intended as an intermediate category between benign and malignant, but rather to denote a finding that has such a low probability of malignancy that a short-term follow-up, usually 6 months, is more appropriate than further diagnostic interventions.
The interpreting physician, referring physician, and patient all have an interest in assuring compliance with this recommendation, because neglecting the short-term follow-up results in adverse consequences in a small percentage of cases. The next two categories are those that warrant a biopsy. Category 4, "suspicious abnormality - biopsy should be considered," is for a lesion that has a definite probability of being malignant; category 5, "highly suggestive of malignancy - appropriate action should be taken," is for a lesion that is very characteristic for malignancy.
At a time after significant progress has been made in lowering dose and improving image quality, a greater understanding of factors associated with higher mammographic accuracy should be a priority for greater data collection and research. With the advent of a standardized lexicon and a more complete understanding of the benefits of a medical audit, obtaining data on the status of interpretation in the United States is a necessary first step. Successful methods of education focused on interpretation skills must be developed and tested both in initial small groups and subsequently in actual practice. Finally, we must develop outcome measures of interpretive performance and identify where weaknesses exist. {pagebreak}
Elmore et al. describe the variability of mammographic interpretation between radiologists and the variability in specificity by age 35. If one examines the variability that they describe, one sees from the receiver operating curves presented that it is along the curve rather than above or below it. This suggests that improvement in interpretive skills to better define features and criteria for biopsy will have a significant beneficial impact on this variability.
Inasmuch as breast cancer is among women's greatest health concerns, test results suggesting that a woman may have breast cancer are likely to cause anxiety, and the anxiety may be greater and more lasting the further along the diagnostic chain her evaluation proceeds. However, in terms of the consequences and resulting anxiety, from a measurement standpoint there is no justification for treating all false-positive results (i.e., FP1–3 or PPV1–3), as equivalent. Elmore reviewed mammographic recall and biopsy data over a 10-year period and observed that 23.8% of women had at least one false-positive mammogram and 31.7% had either a false-positive mammogram or CBE.
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Although relatively high over time (2,227 women had 9,762 examinations over the study period), the rate of false-positive findings by examination was much lower. In other words, the likelihood of a false-positive result is considerably lower per screening event than over the duration of screening events. This is to be expected, and Elmore's study highlights not only that a higher rate of false-positives can be expected with sporadic, opportunistic screening but also the need to identify best practices in order to reduce the rate of avoidable false-positives. Because women are worried about breast cancer, providers must handle any need for extra procedures with great sensitivity. Although avoiding mammography because of the risk of false-positive results has been proposed, a more valuable strategy would assure that women who undergo screening know what to expect. New programs are needed to improve the overall quality of screening and follow-up services, including greater attention to the psychosocial needs of women who have abnormal findings.
An encouraging report and actually the first glimpse of mammography as performed on a national level was presented by May et al. As noted in the discussion of specificity, the report summarizes findings for 230,143 women who underwent mammography during the first 4 years of the National Breast and Cervical Cancer Early Detection Program. When biopsy was recommended from mammography, the PPV was 26%. The suggested goal from the AHCPR panel is 25% to 40%. The rate of prevalent cancers found was 5.1 in 1,000, and the rate of incident cancers was 2.0 per 1,000, a little lower than the AHCPR suggested goals for these parameters of 6 to 10 per 1,000 and 2 to 4 per 1,000, respectively, but overall the CDC screening population was skewed in early years toward a younger population of women. The recall rate was 5%, and the suggested goal is no greater than 10%.
Finally, minimal cancers (invasive tumors less than 1.0 cm and DCIS) comprised 45% of the cancers, with a suggested goal of more than 30%. Thus, what we see from this report is a first view of screening results in the United States that is not limited to academic centers but is probably representative of a broad cross section of our screening efforts. The fact that overall performance by facilities participating in the CDC program falls within the target ranges that were established by the AHCPR panel is encouraging.
Robert A. Smith and Carl J. D'Orsi
R. A. Smith: Cancer Screening, Department of Cancer Control, American Cancer Society, Atlanta, Georgia C. J. D'Orsi: Diagnostic Radiology, University of Massachusetts Memorial Medical Center, Worchester, Massachusetts
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