How accurately can multiparametric magnetic resonance imaging measure the tumour volume of a prostate cancer? Results of a systematic review

The tumour volume of a cancer within the prostate gland is commonly measured with multiparametric MRI. The measurement has a role in many clinical scenarios including focal therapy, but the accuracy of it has never been systematically reviewed. We included articles if they compared tumour volume measurements obtained by mpMRI with a reference volume measurement obtained after radical prostatectomy. Correlation and concordance statistics were summarised. A simple accuracy score was derived by dividing the given mean or median mpMRI volume by the histopathological reference volume. Factors affecting the accuracy were noted. Scores for potential bias and quality were calculated for each article. A total of 18 articles describing 1438 patients were identified. Nine articles gave Pearson's correlation scores, with a median value of 0.75 but the range was wide (0.42-0.97). A total of 11 articles reported mean values for volume while 9 reported median values. For all 18 articles, the mean or median values for MRI volumes were lower than the corresponding reference values suggesting consistent underestimation. For articles reporting mean and median values for volume, the median accuracy scores were 0.83 and 0.80, respectively. The accuracy was higher for tumours of greater volume, higher grade and when an endorectal coil was used. Accuracy did not seem to improve over time, with a 3 Tesla magnet or by applying a shrinkage factor to the reference measurement. Most studies showed evidence of at least moderate bias, and their quality was highly variable, but neither of these appeared to affect accuracy.

Decision models for distinguishing between clinically insignificant and significant tumors in prostate cancer biopsies: an application of Bayes' Theorem to reduce costs and improve outcomes

Prostate cancer is the second leading cause of death from cancer, behind lung cancer, for men in the U. S, with nearly 30,000 deaths per year. A key problem is the difficulty in distinguishing, after biopsy, between significant cancers that should be treated immediately and clinically insignificant tumors that should be monitored by active surveillance. Prostate cancer has been over-treated; a recent European randomized screening trial shows overtreatment rates of 40%. Overtreatment of insignificant tumors reduces quality of life, while delayed treatment of significant cancers increases the incidence of metastatic disease and death. We develop a decision analysis approach based on simulation and probability modeling. For a given prostate volume and number of biopsy needles, our rule is to treat if total length of cancer in needle cores exceeds c, the cutoff value, with active surveillance otherwise, provided pathology is favorable. We determine the optimal cutoff value, c*. There are two misclassification costs: treating a minimal tumor and not treating a small or medium tumor (large tumors were never misclassified in our simulations). Bayes' Theorem is used to predict the probabilities of minimal, small, medium, and large cancers given the total length of cancer found in biopsy cores. A 20 needle biopsy in conjunction with our new decision analysis approach significantly reduces the expected loss associated with a patient in our target population about to undergo a biopsy. Longer needles reduce expected loss. Increasing the number of biopsy cores from the current norm of 10-12 to about 20, in conjunction with our new decision model, should substantially improve the ability to distinguish minimal from significant prostate cancer by minimizing the expected loss from over-treating minimal tumors and delaying treatment of significant cancers.

Impact of a novel biopsy instrument with a 25-mm side-notch needle on the detection of prostate cancer in transrectal biopsy

OBJECTIVES

To evaluate the impact of a novel biopsy instrument that extends the length of the side-notch on the detection of prostate cancer in transrectal needle biopsy.

METHODS

We collaborated with a biopsy needle manufacturer and developed a novel biopsy instrument (PRIMECUT II long-notch type) with a 25-mm side-notch length and 28-mm stroke length to take longer tissue cores. The sampled core length, cancer detection rate, pain and complications of 489 patients who underwent transrectal biopsy using the long-notch needle were compared with those of 469 patients who underwent biopsy using a normal instrument with a 19-mm side-notch length and 22-mm stroke length.

RESULTS

The mean length of tissue taken by the long-notch needle was significantly longer than that of tissue taken by the normal-notch needle (16.3 vs 22.4 mm, P < 0.001). The overall cancer detection rate was 42.0% for the normal-notch needle and 51.1% for the long-notch needle (P = 0.005). In patients with a prostate volume of 20-40 mL, the cancer detection rate for the long-notch needle was especially higher than that for the normal-notch needle (74.2% vs 47.5%, P < 0.001). Multivariate analysis showed that the long-notch needle improved cancer detection significantly (odds ratio 1.702, P < 0.001). There were no differences of pain during biopsy and complication between the two groups.

CONCLUSIONS

The novel biopsy instrument with a 25-mm side-notch can take longer tissue samples safely and has a significantly higher rate of prostate cancer detection in transrectal biopsy.