PROSTATE CANCER: THE ROLE OF TRANSRECTAL ULTRASOUND AND ITS IMPACT ON CANCER DETECTION AND MANAGEMENT

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Transrectal ultrasound (TRUS) has undergone a continuous evolutionary process, in part owing to continued advances in computer and transducer components. The pace of technologic advancement, however, sometimes exceeds our clinical abilities to ascertain its benefit. In addition, there has been a tendency to view diagnostic parameters on an individual basis, rather than as a continuum of additive risk factors. TRUS was crucial in revolutionizing prostate biopsy techniques, yet its role in diagnosis and individual risk assessment has been more controversial. Political incentives and medical territoriality have played a role, but there is little question about the operator-dependent nature of ultrasound. This may be especially true for TRUS because equipment quality and operator experience vary significantly from tertiary medical facilities to private offices. It is, therefore, important to understand the effects of multiple different risk factors on biopsy outcomes.

The American College of Radiology, the American Urologic Association, and the American Cancer Society have recommended that TRUS evaluation be limited to patients with either abnormal digital rectal examination (DRE) or elevated prostate-specific antigen (PSA) level. The assessment of prostate cancer (PCa) risk factors thus begins before TRUS examination and includes positive family history, race, and age. All of these parameters affect pretest probability of cancer being present, yet few physicians (let alone ultrasound technologists) attempt to assess TRUS findings in relation to individual patient risk criteria. Therefore, this article focuses on more than descriptive TRUS findings and presents the impact of other risk factors on the likelihood of biopsy revealing cancer. Perhaps many debates surrounding the test performance of TRUS findings or biopsy outcomes could be mollified if these pretest probabilities could be viewed on a relative risk gradient, or continuum. In this manner, it may become easier to understand the rationale for more tailored biopsy strategies18 that will continue to emerge as more patient-specific testing allows for easier clinical application. In other words, thorough understanding of each patient's risk for prostate cancer is just as important as understanding the likelihood of any TRUS finding being worthy of a targeted biopsy in that region.

Section snippets

EPIDEMIOLOGIC AND CLINICAL ISSUES

Understanding diagnostic test performance requires a basic review of frequently used statistical parameters and their impact on decision making in the work-up of prostate cancer patients.

  • True positives=TP; false-positives=FP; true-negatives=TN; false-negatives=FN

  • Sensitivity = TP/(TP + FN)

  • Specificity = TN/(TN + FP)

  • Positive predictive value = TP/(TP + FP)

  • Negative predictive value = TN/(TN + FN)

  • Accuracy = (TP + TN)/(TP + FP + TN + FN)

Sensitivity is thus primarily driven by false-negatives,

Technique

The advent of high-frequency transducers provided the necessary improvement in spatial resolution to allow a detailed view of internal prostate anatomy. The majority of papers published before 1986 used ultrasound transducers operating at 3.5 and 4 MHz. These images of the prostate produced criteria for cancer, which relied on the evaluation of the external contours of the gland for asymmetry, prostate diameter, and distortion of the capsule.6, 31 With newer 5- and 7-MHz transducers, the basic

SUMMARY

With the advent of higher-frequency transducers as well as Doppler technologies, TRUS has become a valuable tool in the detection and management of prostate cancer. When combined with the other risk identifiers, an informed patient, and an experienced operator, it cannot only reduce the number of missed cancers by effective targeting of biopsies, but also reduce the number of unnecessary biopsies.

ACKNOWLEDGMENTS

The authors express their thanks to Kyle Meetz, BS, and Faith Howard, BA, for their assistance in the preparation of this manuscript.

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