The ultrasound probe used during biopsy may affect diagnosis

There are two basic types of transrectal ultrasound probe most commonly used to monitor positioning of biopsy needles during the biopsy procedure — the so-called “side fire” and “end fire” types. A recent analysis of data from the Cleveland Clinic suggests that the type of ultrasound probe used may significantly affect the likelihood of diagnosis.

Ching et al. evaluated data from 2,674 patients who underwent initial prostate biopsy between 2000 and 2008 with respect to PSA level, biopsy technique, and pathological findings. Patients included 1,124 in whom biopsies were performed with an end fire probe and 1,550 in whom biopsies were performed with a side fire probe.

The results of the evaluation are as follows:

  • There was a significant difference in the overall cancer detection rate between patients in the end fire vs the side fire groups (45.8 vs 38.5 percent).
  • This significant difference was also evident in two subsets of patients
    • Those with PSA levels between > 4 and ≤ 10 ng/ml (46.4 vs 38.9 percent)
    • Those with PSA levels > 10 ng/ml (61.7 vs 49.1 percent)
  • There was a significant difference in detection rates between probes in those patients who had between 8 and 19 biopsy cores taken.
  • If ≥ 20 cores were taken, there was no statistically significance difference in the results between the two types of probe.
  • Prostate volume, patient age, PSA level, and hypoechoic findings were all independent variables for predicting cancer detection on multivariate analysis.

The authors conclude that the type of probe significantly affects the overall prostate cancer detection rate, particularly in patients who have PSA levels > 4 ng/ml and/or nonsaturation prostate biopsies (with 8 to 19 cores).

The authors suggest that this result may occur because the end fire probe allows better mechanical sampling of the lateral and apical regions of the peripheral zone, where cancer is most likely to reside. They suggest that these data “set the stage” for a randomized clinical trial of the two types of biopsy, but The “New” Prostate Cancer InfoLink wonders whether such a trial is ethical, given the large degree of statistical significance between the biopsy results using these two different types of probe.

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