Mapping of transrectal ultrasonographic prostate biopsies: quality control and learning curve assessment by image processing

External validation of a prostate biopsy simulator

INTRODUCTION

Simulation-based training has proven to be a promising option allowing for initial and continuous training while limiting the impact of the learning curve on the patient. The Biopsym simulator was developed as a complete teaching environment for the prostate biopsy procedure. This paper presents the results of an external validation of this simulator, involving urology residents recruited during a regional teaching seminar.

METHODS

Residents from 4 academic urology departments of the French Auvergne Rhône-Alpes region, who did not take part in the previous simulator validation studies, were enrolled. After a short presentation and standardized initiation session, residents carried out a simulated systematic 12-core biopsy procedure and were asked to fill in a questionnaire collecting their expectations and evaluation of the Biopsym simulator. The number of biopsies reaching each targeted sector, the total score provided by the simulator and the duration of the procedure were recorded.

RESULTS

Twenty-three residents were recruited. The overall added value (/100) for learning was rated at a median of 100 (interquartile range 83-100), overall realism of the biopsy procedure at 80 (65-89). The median percentage of biopsies reaching the targeted sector was 66.7% (62-75). The median score provided by the simulator was 50% (37-60). For both, the difference between residents with or without prior biopsy experience was not statistically significant. The median duration of the simulated biopsy procedure was 4:58 (minutes: seconds) (3:49-6:00). Resident with prior experience required less time to complete the biopsy procedure 3:53 (3:39-4:56) vs. 5:10 (4:59-7:10), P=0.01.

CONCLUSION

This external validation study confirms a high acceptance of the simulator by the target audience. To our knowledge, the Biopsym simulator is the only prostate biopsy simulator that demonstrated such validity as evaluated by clinicians, outside the center involved in its early development.

LEVEL OF EVIDENCE

3.

Attitude is everything: keep probe pitch neutral during side-fire prostate biopsy. A simulator study

OBJECTIVES

To develop and validate on a simulator a learnable technique to decrease deviation of biopsied cores from the template schema during freehand, side-fire systematic prostate biopsy (sPBx) with the goal of reducing prostate biopsy (PBx) false-negatives, thereby facilitating earlier sampling, diagnosis and treatment of clinically significant prostate cancer.

PARTICIPANTS AND METHODS

Using a PBx simulator with real-time three-dimensional visualization, we devised a freehand, pitch-neutral (0°, horizontal plane), side-fire, transrectal ultrasonography (TRUS)-guided sPBx technique in the left lateral decubitus position. Thirty-four trainees on four Canadian and US urology programmes learned the technique on the same simulator, which recorded deviation from the intended template location in a double-sextant template as well as the TRUS probe pitch at the time of sampling. We defined deviation as the shortest distance in millimeters between a core centre and its intended template location, template deviation as the mean of all deviations in a template, and mastery as achieving a template deviation ≤5.0 mm.

RESULTS

All results are reported as mean ± sd. The mean absolute pitch and template deviation before learning the technique (baseline) were 8.2 ± 4.1° and 8.0 ± 2.7 mm, respectively, and after mastering the technique decreased to 4.5 ± 2.7° (P = 0.001) and 4.5 ± 0.6 mm (P < 0.001). Template deviation was related to mean absolute pitch (P < 0.001) and increased by 0.5 mm on average with each 1° increase in mean absolute pitch. Participants achieved mastery after practising 3.9 ± 2.9 double-sextant sets. There was no difference in time to perform a double-sextant set at baseline (277 ± 102 s) and mastery (283 ± 101 s; P = 0.39).

CONCLUSION

A pitch-neutral side-fire technique reduced template deviation during simulated freehand TRUS-guided sPBx, suggesting it may also reduce PBx false-negatives in patients in a future clinical trial. This pitch-neutral technique can be taught and learned; the University of Florida has been teaching it to all Urology residents for the last 2 years.

Validating the Transfer of Skills Acquired on a Prostate Biopsy Simulator: A Prospective, Randomized, Controlled Study

OBJECTIVES

To evaluate the ability of students to reproduce the skills acquired on a prostate biopsy simulator in a real-life situation.

DESIGN

A prospective randomized controlled study was conducted. Medical students with no experience of prostate biopsy were randomized between arm A « conventional training » and arm B « simulator-enhanced training. » The training was performed for both groups on the simulator. The students in arm B were provided with visual and numerical feedback. The transfer of skills was assessed by recording the position of the 12 biopsies performed by each student on an unembalmed human cadaver using a 3D ultrasound mapping device.

SETTING

The study was conducted in an academic urology department and the cadaver experiments in the adjoining anatomy laboratory.

RESULTS

Twenty-four students were included, and 22 completed the study. The median score obtained on the simulator at the end of the training was 57% (53-61) for arm A and 66% (59-71) for arm B. The median score obtained on the cadaver by students trained with the simulator was 75% (60-80), statistically superior to the score obtained by students trained conventionally of 45% (30-60), p < 0.0001. The median score obtained by all students when performing biopsies in a real-life situation was 63% (50-80) versus 60% (56-70) for their last training on the simulator.

CONCLUSION

These results support the transfer of skills acquired on the simulator, and the superiority of a training curriculum integrating simulation, and performance feedback.

Robotic Transrectal Ultrasound Guided Prostate Biopsy

We present a robot-assisted approach for transrectal ultrasound (TRUS) guided prostate biopsy. The robot is a hands-free probe manipulator that moves the probe with the same 4 DoF that are used manually. Software was developed for three-dimensional (3-D) imaging, biopsy planning, robot control, and navigation. Methods to minimize the deformation of the prostate caused by the probe at 3-D imaging and needle targeting were developed to reduce biopsy targeting errors. We also present a prostate coordinate system (PCS). The PCS helps defining a systematic biopsy plan without the need for prostate segmentation. Comprehensive tests were performed, including two bench tests, one imaging test, two in vitro targeting tests, and an IRB-approved clinical trial on five patients. Preclinical tests showed that image-based needle targeting can be accomplished with accuracy on the order of 1 mm. Prostate biopsy can be accomplished with minimal TRUS pressure on the gland and submillimetric prostate deformations. All five clinical cases were successful with an average procedure time of 13 min and millimeter targeting accuracy. Hands-free TRUS operation, transrectal TRUS guided prostate biopsy with minimal prostate deformations, and the PCS-based biopsy plan are novel methods. Robot-assisted prostate biopsy is safe and feasible. Accurate needle targeting has the potential to increase the detection of clinically significant prostate cancer.

3D Registration of mpMRI for Assessment of Prostate Cancer Focal Therapy

RATIONALE AND OBJECTIVES

This study aimed to assess a novel method of three-dimensional (3D) co-registration of prostate magnetic resonance imaging (MRI) examinations performed before and after prostate cancer focal therapy.

MATERIALS AND METHODS

We developed a software platform for automatic 3D deformable co-registration of prostate MRI at different time points and applied this method to 10 patients who underwent focal ablative therapy. MRI examinations were performed preoperatively, as well as 1 week and 6 months post treatment. Rigid registration served as reference for assessing co-registration accuracy and precision.

RESULTS

Segmentation of preoperative and postoperative prostate revealed a significant postoperative volume decrease of the gland that averaged 6.49 cc (P = .017). Applying deformable transformation based on mutual information from 120 pairs of MRI slices, we refined by 2.9 mm (max. 6.25 mm) the alignment of the ablation zone, segmented from contrast-enhanced images on the 1-week postoperative examination, to the 6-month postoperative T2-weighted images. This represented a 500% improvement over the rigid approach (P = .001), corrected by volume. The dissimilarity by Dice index of the mapped ablation zone using deformable transformation vs rigid control was significantly (P = .04) higher at the ablation site than in the whole gland.

CONCLUSIONS

Our findings illustrate our method's ability to correct for deformation at the ablation site. The preliminary analysis suggests that deformable transformation computed from mutual information of preoperative and follow-up MRI is accurate in co-registration of MRI examinations performed before and after focal therapy. The ability to localize the previously ablated tissue in 3D space may improve targeting for image-guided follow-up biopsy within focal therapy protocols.

[Interest using 3D ultrasound and MRI fusion biopsy for prostate cancer detection]

INTRODUCTION

The strategic therapy for prostate cancer depends on histo-pronostics data, which could be upgraded by obtaining targeted biopsies (TB) with MRI (magnetic resonance imagery) fusion 3D ultrasound.

OBJECTIVES

To compare diagnostic yield of image fusion guided prostate biopsy using image fusion of multi-parametric MRI (mpMRI) with 3D-TRUS.

MATERIALS AND METHODS

Between January 2010 and April 2013, 179 consecutive patients underwent outpatient TRUS biopsy using the real-time 3D TRUS tracking system (Urostation™). These patients underwent MRI-TRUS fusion targeted biopsies (TB) with 3D volume data of the MRI elastically fused with 3D TRUS at the time of biopsy.

RESULTS

A hundred and seventy-three patients had TBs with fusion. Mean biopsy core per patient were 11.1 (6-14) for SB and 2.4 (1-6) for TB. SBs were positive in 11% compared to 56% for TB (P<0.001). TB outperformed systematic biopsy(SB) in overall any cancer detection rate, detection of clinically significant cancer (58% vs. 36%), cancer core length (6.8mm vs. 2.8mm), and cancer rate per core (P<0.001). In multivariable logistic regression, with TB we have more chance to find a clinically significant cancer (OR:3.72 [2-6.95]). When both TRUS and MRI are positive, there is 2.73 more chance to find a clinically significant cancer.

CONCLUSION

MR/TRUS elastic fusion-guided biopsies outperform systematic random biopsies in diagnosing clinically significant cancer. Ability of interpretation of real-time TRUS is essential to perform the higher level of MR/US fusion and should be use for active surveillance.

LEVEL OF PROOF

4.

MR-TRUS Fusion Biopsy

The leading application of multiparametric magnetic resonance imaging (mpMRI) of the prostate is for lesion detection with the intention of tissue sampling (biopsy). Although direct in-bore magnetic resonance (MR)-guided biopsy allows for confirmation of the biopsy site, this can be expensive, time-consuming, and most importantly limited in availability. MR-transrectal ultrasound (MR-TRUS) image fusion targeted biopsy (TBx) allows for lesions identified on MRI to be targeted with the ease, efficiency, and availability of ultrasound.The learning objectives are optimized mpMRI protocol and reporting for image fusion targeted biopsy; methods of TRUS TBx; performance and limitations of MR-TRUS TBx; future improvements and applications.

A novel technique using three-dimensionally documented biopsy mapping allows precise re-visiting of prostate cancer foci with serial surveillance of cell cycle progression gene panel

BACKGROUND

Conventional systematic biopsy has the shortcoming of sampling error and reveals "no evidence of cancer" with a rate of >50% on active surveillance (AS). The objective of this study is to report our initial experience of applying a 3D-documented biopsy-mapping technology to precisely re-visit geographically documented low-risk prostate cancer and to perform serial analysis of cell-cycle-progression (CCP) gene-panel.

METHODS

Over a period of 40 months (1/2010-4/2013), the 3D-biopsy-mapping technique, in which the spatial location of biopsy-trajectory was digitally recorded (Koelis), was carried out. A pair of diagnostic (1st-look) and surveillance (2nd-look) biopsy were performed per subject (n = 25), with median interval of 12 months. The documented biopsy-trajectory was used as a target to guide the re-visiting biopsy from the documented cancer focus, as well as the targeted field-biopsy from the un-sampled prostatic field adjacent to negative diagnostic biopsies. The accuracy of re-visiting biopsy and biopsy-derived CCP signatures were evaluated in the pair of the serial biopsy-cores.

RESULTS

The 1st-look-biopsy revealed a total of 43 cancer lesions (1.7 per patient). The accuracy of re-visiting cancer was 86% (37/43) per lesion, 76% (65/86) per core, and 80% (20/25) per patient. This technology also provided an opportunity for 3D-targeted field-biopsy in order to potentially minimize sampling errors. The CCP gene-panel of the 1st-look (-0.59) versus 2nd-look (-0.37) samples had no significant difference (P = 0.4); which suggested consistency in the molecular signature of the known cancer foci during the short-time interval of median 12 months. Any change in CCP of the same cancer foci would be likely due to change in sampling location from the less to more significant portion in the cancer foci rather than true molecular progression. The study limitations include a small number of the patients.

CONCLUSION

The 3D-documented biopsy-mapping technology achieved an encouraging re-sampling accuracy of 86% from the known prostate cancer foci, allowing the serial analysis of biopsy-derived CCP signatures.

Novel trends in transrectal ultrasound imaging of prostate gland carcinoma

Carcinoma of the prostate gland is the most common neoplasm in men. Its treatment depends on multiple factors among which local staging plays a significant role. The basic method is transrectal ultrasound imaging. This examination enables imaging of the prostate gland and its abnormalities, but it also allows ultrasound-guided biopsies to be conducted. A conventional gray-scale ultrasound examination enables assessment of the size, echostructure and outlines of the anatomic capsule, but in many cases, neoplastic lesions cannot be observed. For this reason, new sonographic techniques are implemented in order to facilitate detectability of cancer. The usage of contrast agents during transrectal ultrasound examination must be emphasized since, in combination with color Doppler, it facilitates detection of cancerous lesions by visualizing flow which is not observable without contrast enhancement. Elastography, in turn, is a different solution. It uses the differences in tissue elasticity between a neoplastic region and normal prostatic parenchyma that surrounds it. This technique facilitates detection of lesions irrespective of their echogenicity and thereby supplements conventional transrectal examinations. However, the size of the prostate gland and its relatively far location from the transducer may constitute limitations to the effectiveness of elastography. Moreover, the manner of conducting such an examination depends on the examiner and his or her subjective assessment. Another method, which falls within the novel, popular trend of combining imaging methods, is fusion of magnetic resonance imaging and transrectal sonography. The application of multidimensional magnetic resonance imaging, which is currently believed to be the best method for prostate cancer staging, in combination with the availability of a TRUS examination and the possibility of monitoring biopsies in real-time sonography is a promising alternative, but it is associated with higher costs and longer duration of the examination. This paper presents the most important novel trends in transrectal imaging in prostate cancer diagnosis based on the review of the articles available in the PubMed base and published after 2010.

First round of targeted biopsies using magnetic resonance imaging/ultrasonography fusion compared with conventional transrectal ultrasonography-guided biopsies for the diagnosis of localised prostate cancer

OBJECTIVES

To assess the accuracy of magnetic resonance imaging (MRI)/transrectal ultrasonography (TRUS) fusion to guide first-round biopsies in the diagnosis of localised prostate cancer (PCa) in men with a prostate-specific antigen (PSA) ≤10 ng/mL.

PATIENTS AND METHODS

A prospective study was conducted on men who met the following criteria: first-round biopsy, multiparametric MRI (mpMRI) showing a lesion with a Likert score ≥2 and a PSA <10 ng/mL. All men underwent a extended 12-core protocol plus a protocol of two or three targeted cores on the mpMRI index lesion. The UroStation (Koelis, Grenoble, France) and a V10 ultrasound system with an end-fire three-dimensional TRUS transducer were used for the fusion imaging procedure. Significant PCa was defined as: at least one core with a Gleason score of 3 + 4 or 6 with a maximum cancer core length ≥4 mm.

RESULTS

A total of 152 men, whose median PSA level was 6 ng/mL, were included in the study. The proportion of positive cores was significantly higher with the targeted-core protocol than with the extended 12-core protocol (P < 0.001). The proportion of men with clinically significant PCa was higher with the targeted-core protocol than with the extended 12-core protocol (P = 0.03). The proportion of patients having at least one positive biopsy (targeted-core protocol) was significantly different among the Likert score categories (P < 0.001).

CONCLUSIONS

For the first round of biopsies, MRI/TRUS-fusion targeted biopsies detected more men with clinically significant PCa than did standard extended 12-core biopsy alone.

Robotic ultrasound and needle guidance for prostate cancer management: review of the contemporary literature

PURPOSE OF REVIEW

To present the recent advances in needle guidance and robotic ultrasound technology which are used for prostate cancer (PCa) diagnosis and management.

RECENT FINDINGS

Prostate biopsy technology has remained relatively unchanged. Improved needle localization and precision would allow for better management of this common disease. Robotic ultrasound and needle guidance is one strategy to improve needle localization and diagnostic accuracy of PCa. This review focuses on the recent advances in robotic ultrasound and needle guidance technologies, and their potential impact on PCa diagnosis and management.

SUMMARY

The use of robotic ultrasound and robotic-assisted needle guidance has the potential to improve PCa diagnosis and management.

3D versus 2D Systematic Transrectal Ultrasound-Guided Prostate Biopsy: Higher Cancer Detection Rate in Clinical Practice

Objectives. To compare prostate cancer detection rates of extended 2D versus 3D biopsies and to further assess the clinical impact of this method in day-to-day practice. Methods. We analyzed the data of a cohort of 220 consecutive patients with no prior history of prostate cancer who underwent an initial prostate biopsy in daily practice due to an abnormal PSA and/or DRE using, respectively, the classical 2D and the new 3D systems. All the biopsies were done by a single experienced operator using the same standardized protocol. Results. There was no significant difference in terms of age, total PSA, or prostate volume between the two groups. However, cancer detection rate was significantly higher using the 3D versus the 2D system, 50% versus 34% (P < 0.05). There was no statistically significant difference while comparing the 2 groups in term of nonsignificant cancer detection. Conclusion. There is reasonable evidence demonstrating the superiority of the 3D-guided biopsies in detecting prostate cancers that would have been missed using the 2D extended protocol.

Targeted MRI-guided prostate biopsies for the detection of prostate cancer: initial clinical experience with real-time 3-dimensional transrectal ultrasound guidance and magnetic resonance/transrectal ultrasound image fusion

OBJECTIVE

To prove the feasibility and evaluate the initial clinical results of targeted prostate biopsies using the Urostation novel platform using magnetic resonance imaging (MRI)/transrectal ultrasound (TRUS) registration to help steer the biopsy needle to suspicious areas.

METHODS

We prospectively included 30 patients for suspicion of prostate cancer from November 2011 to August 2012. All patients were previously evaluated by a multiparametric MRI, interpreted by a single radiologist who attributed a Prostate Imaging-Reporting and Data System (PI-RADS) score to each lesion. A conventional 12-core randomized biopsy protocol was performed and 2 additional targeted biopsies were performed on suspicious area(s). The results of randomized and targeted biopsies were compared.

RESULTS

Among the 30 patients, suspicious area(s) were found on MRI in 20 cases (67%). Median procedure time was 23 minutes. Targeting success rate (biopsy visualized inside the target) was 83%, with at least 1 biopsy reaching the target in all cases. Prostate cancer was detected in 14 cases (47%), including 11 cases with an abnormal MRI. Targeted biopsies detected cancer in all 11 cases and all but 1 were clinically significant. Randomized biopsies detected 10 of these 11 cases, and 3 more cases that MRI considered normal. Sensitivity to detect a significant cancer was 91% in both modalities.

CONCLUSION

This initial clinical study showed encouraging results for targeted MRI-guided prostate biopsies using MRI-TRUS fusion. Although further studies are needed to determine the role of prostate MRI before biopsy and the relevance of targeted biopsies, the Urostation is an MRI-TRUS fusion device that has good accuracy for targeting suspicious areas on MRI.

Ultrasound probe and needle-guide calibration for robotic ultrasound scanning and needle targeting

Image-to-robot registration is a typical step for robotic image-guided interventions. If the imaging device uses a portable imaging probe that is held by a robot, this registration is constant and has been commonly named probe calibration. The same applies to probes tracked by a position measurement device. We report a calibration method for 2-D ultrasound probes using robotic manipulation and a planar calibration rig. Moreover, a needle guide that is attached to the probe is also calibrated for ultrasound-guided needle targeting. The method is applied to a transrectal ultrasound (TRUS) probe for robot-assisted prostate biopsy. Validation experiments include TRUS-guided needle targeting accuracy tests. This paper outlines the entire process from the calibration to image-guided targeting. Freehand TRUS-guided prostate biopsy is the primary method of diagnosing prostate cancer, with over 1.2 million procedures performed annually in the U.S. alone. However, freehand biopsy is a highly challenging procedure with subjective quality control. As such, biopsy devices are emerging to assist the physician. Here, we present a method that uses robotic TRUS manipulation. A 2-D TRUS probe is supported by a 4-degree-of-freedom robot. The robot performs ultrasound scanning, enabling 3-D reconstructions. Based on the images, the robot orients a needle guide on target for biopsy. The biopsy is acquired manually through the guide. In vitro tests showed that the 3-D images were geometrically accurate, and an image-based needle targeting accuracy was 1.55 mm. These validate the probe calibration presented and the overall robotic system for needle targeting. Targeting accuracy is sufficient for targeting small, clinically significant prostatic cancer lesions, but actual in vivo targeting will include additional error components that will have to be determined.

Prostate cancer risk inflation as a consequence of image-targeted biopsy of the prostate: a computer simulation study

Background

Prostate biopsy parameters are commonly used to attribute cancer risk. A targeted approach to lesions found on imaging may have an impact on the risk attribution given to a man.

Objective

To evaluate whether, based on computer simulation, targeting of lesions during biopsy results in reclassification of cancer risk when compared with transrectal ultrasound (TRUS) guided biopsy.

Design, setting, and participants

A total of 107 reconstructed three-dimensional models of whole-mount radical prostatectomy specimens were used for computer simulations. Systematic 12-core TRUS biopsy was compared with transperineal targeted biopsies using between one and five cores. All biopsy strategies incorporated operator and needle deflection error. A target was defined as any lesion ≥0.2 ml. A false-positive magnetic resonance imaging identification rate of 34% was applied.

Outcome measurements and statistical analysis

Sensitivity was calculated for the detection of all cancer and clinically significant disease. Cases were designated as high risk based on achieving ≥6 mm cancer length and/or ≥50% positive cores. Statistical significance (p values) was calculated using both a paired Kolmogorov-Smirnov test and the t test.

Results and limitations

When applying a widely used biopsy criteria to designate risk, 12-core TRUS biopsy classified only 24% (20 of 85) of clinically significant cases as high risk, compared with 74% (63 of 85) of cases using 4 targeted cores. The targeted strategy reported a significantly higher proportion of positive cores (44% vs 11%; p < 0.0001) and a significantly greater mean maximum cancer core length (7.8 mm vs 4.3 mm; p < 0.0001) when compared with 12-core TRUS biopsy. Computer simulations may not reflect the sources of errors encountered in clinical practice. To mitigate this we incorporated all known major sources of error to maximise clinical relevance.

Conclusions

Image-targeted biopsy results in an increase in risk attribution if traditional criteria, based on cancer core length and the proportion of positive cores, are applied. Targeted biopsy strategies will require new risk stratification models that account for the increased likelihood of sampling the tumour.

Geometric evaluation of systematic transrectal ultrasound guided prostate biopsy

PURPOSE

Transrectal ultrasound guided prostate biopsy results rely on physician ability to target the gland according to the biopsy schema. However, to our knowledge it is unknown how accurately the freehand, transrectal ultrasound guided biopsy cores are placed in the prostate and how the geometric distribution of biopsy cores may affect the prostate cancer detection rate.

MATERIALS AND METHODS

To determine the geometric distribution of cores, we developed a biopsy simulation system with pelvic mock-ups and an optical tracking system. Mock-ups were biopsied in a freehand manner by 5 urologists and by our transrectal ultrasound robot, which can support and move the transrectal ultrasound probe. We compared 1) targeting errors, 2) the accuracy and precision of repeat biopsies, and 3) the estimated significant prostate cancer (0.5 cm(3) or greater) detection rate using a probability based model.

RESULTS

Urologists biopsied cores in clustered patterns and under sampled a significant portion of the prostate. The robot closely followed the predefined biopsy schema. The mean targeting error of the urologists and the robot was 9.0 and 1.0 mm, respectively. Robotic assistance significantly decreased repeat biopsy errors with improved accuracy and precision. The mean significant prostate cancer detection rate of the urologists and the robot was 36% and 43%, respectively (p <0.0001).

CONCLUSIONS

Systematic biopsy with freehand transrectal ultrasound guidance does not closely follow the sextant schema and may result in suboptimal sampling and cancer detection. Repeat freehand biopsy of the same target is challenging. Robotic assistance with optimized biopsy schemas can potentially improve targeting, precision and accuracy. A clinical trial is needed to confirm the additional benefits of robotic assistance.

Elastic image registration for guiding focal laser ablation of prostate cancer: preliminary results

PURPOSE

To guide ultrasound-driven prostate photodynamic therapy using information from MRI-based treatment planning.

METHODS

Robust points matching (RPM) and thin plate splines (TPS) are used to solve correspondences and to map optimally positioned landmarks from MR images to transrectal ultrasound (TRUS) images. The algorithm uses a reduced number of anatomical markers that are initialized on the images.

RESULTS

Both phantom and patient data were used to evaluate precision and robustness of the method. Mean registration error (±standard deviation) was of 2.18±0.25 mm and 1.55±0.31 mm for patient prostate and urethra, respectively. Repeated tests with different markers initialization conditions showed that the quality of registration was neither influenced by the number of markers nor to the human observer.

CONCLUSION

This method allows for satisfyingly accurate and robust non rigid registration of MRI and TRUS and provides practitioners with substantial help in mapping treatment planning from pre-operative MRI to interventional TRUS.

A biopsy simulation study to assess the accuracy of several transrectal ultrasonography (TRUS)-biopsy strategies compared with template prostate mapping biopsies in patients who have undergone radical prostatectomy

What's known on the subject? and What does the study add? Transrectal ultrasonography (TRUS)-guided biopsies can miss prostate cancer and misclassify risk in a diagnostic setting; the exact extent to which it does so in a repeat biopsy strategy in men with low-intermediate risk prostate cancer is unknown. A simulation study of different biopsy strategies showed that repeat 12-core TRUS biopsy performs poorly. Adding anterior sampling improves on this but the highest accuracy is achieved using transperineal template prostate mapping using a 5 mm sampling frame.

OBJECTIVE

To determine the effectiveness of two sampling strategies; repeat transrectal ultrasonography (TRUS)-biopsy and transperineal template prostate mapping (TPM) to detect and exclude lesions of ≥0.2 mL or ≥0.5 mL using computer simulation on reconstructed three-dimensional (3-D) computer models of radical whole-mount specimens.

PATIENTS AND METHODS

Computer simulation on reconstructed 3-D computer models of radical whole-mount specimens was used to evaluate the performance characteristics of repeat TRUS-biopsy and TPM to detect and exclude lesions of ≥0.2 mL or ≥0.5 mL. In all, 107 consecutive cases were analysed (1999-2001) with simulations repeated 500 times for each biopsy strategy. TPM and five different TRUS-biopsy strategies were simulated; the latter involved a standard 12-core sampling and incorporated variable amounts of error, as well as the addition of anterior cores. Sensitivity, specificity, negative and positive predictive values for detection of lesions with a volume of ≥0.2 mL or ≥0.5 mL were calculated.

RESULTS

The mean (SD) age and PSA concentration were 61 (6.4) years and 8.5 (5.9) ng/mL, respectively.In all, 53% (57/107) had low-intermediate risk disease. In all, 665 foci were reconstructed; there were 149 foci ≥0.2 mL and 97 ≥ 0.5 mL in the full cohort and 68 ≥ 0.2 mL and 43 ≥ 0.5 mL in the low-intermediate risk group. Overall, TPM accuracy (area under the receiver operating curve, AUC) was ≈0.90 compared with AUC 0.70-0.80 for TRUS-biopsy. In addition, at best, TRUS-biopsy missed 30-40% of lesions of ≥0.2 mL and ≥0.5 mL whilst TPM missed 5% of such lesions.

CONCLUSION

TPM under simulation conditions appears the most effective re-classification strategy, although augmented TRUS-biopsy techniques are better than standard TRUS-biopsy.

A direct comparison of the diagnostic accuracy of three prostate cancer nomograms designed to predict the likelihood of a positive initial transrectal biopsy

BACKGROUND

Several tools have been developed to predict the outcome of prostate biopsies performed to diagnosis prostate cancer (PCa). However, few studies have focused on the comparative accuracy of these predictive tools. We aim to establish the predictive accuracy of three commonly used nomograms by comparing their prostate biopsy outcome predictions with actual pathological results.

METHODS

From January 2008 to December 2010, 708 consecutive patients with an elevated serum PSA level and/or abnormal DRE were referred to our institution. All data were collected prospectively. All patients underwent a TRUS 12-core biopsy. Probability of a positive biopsy was predicted using three online risk calculation nomograms. The discriminative ability of the nomograms was assessed via AUC and the most accurate model was calibrated and compared to actual biopsy results.

RESULTS

Of 667 patients fulfilling all three nomograms criteria, 384 (57.5%) had PCa and 283 (42.5%) did not. AUC for the PCPT-CRC, SWOP-PRI, and Montreal nomograms was 0.68 (95% CI, 0.63-0.72), 0.72 (95% CI, 0.68-0.76), and 0.79 (95% CI, 0.76-0.82), respectively. A comparison of the three models' performance showed that the Montreal model provided the greatest predictive accuracy (P = 0.03).

CONCLUSIONS

External validation of three commonly used nomograms designed to predict the likelihood of a positive prostate biopsy reveals the Montreal model was more accurate than either the PCPT-CRC or SWOP-PRI models. The Montreal nomogram achieves a diagnostic accuracy of 79% and is superior to PSA alone though we await further research to define the probability (of cancer) threshold above which a prostate biopsy would be advised.

[Accuracy of prostate biopsies to evaluate tumor location in prostate cancer]

INTRODUCTION

The therapeutic approach of prostate cancer depends mainly on pathological criteria obtained through prostate biopsy. The low accuracy of prostate biopsy for Gleason grade determination is well known but its accuracy for bilateral or multifocal tumor has not been evaluated. The goal of this study was to assess the concordance between prostate biopsy and whole prostate specimen obtained after radical prostatectomy especially for bilateral and/or multifocal tumor.

METHODS

We retrospectively compared the pathological results of prostate biopsy cores to the prostate specimen in patients who underwent radical prostatectomy in our department between the 01/01/1999 and the 31/12/2008. The criteria analyzed were the Gleason score, tumor bilaterality or multifocality. The impact of the number of prostate biopsy cores was also analyzed.

RESULTS

Two hundred and five complete histological records were studied. Regarding the Gleason score overall concordance was 55%. In 38%, prostate biopsies downgraded the Gleason score. This concordance decreased with tumor differentiation (90.6% for Gleason 6 vs. 31% for Gleason greater than 7). For the tumor bilaterality, 78% of cancers affected both lobes at the definitive specimen analysis while only 49% were bilateral at prostate biopsies, achieving a concordance of 61%. Multifocal disease was observed in 36% at definitive pathology analysis with low concordance with prostate biopsies (36%). The number of biopsies increased the concordance for the Gleason score (60 to 81% for Gleason 7 and from 28 to 50% for Gleason greater than 7) and tumor location (44 to 70%).

CONCLUSION

Pathological criteria and tumor mapping obtained from prostate biopsies were not very reliable especially when the tumor was poorly differentiated. An increased number of prostate biopsy core improved the sensitivity and specificity for the Gleason score diagnostic and of the tumor mapping.

Is it possible to model the risk of malignancy of focal abnormalities found at prostate multiparametric MRI?

OBJECTIVE

To evaluate whether focal abnormalities (FAs) depicted by prostate MRI could be characterised using simple semiological features.

METHODS

134 patients who underwent T2-weighted, diffusion-weighted and dynamic contrast-enhanced MRI at 1.5 T before prostate biopsy were prospectively included. FAs visible at MRI were characterised by their shape, the degree of signal abnormality (0 = normal to 3 = markedly abnormal) on individual MR sequences, and a subjective score (SS(1) = probably benign to SS(3) = probably malignant). FAs were then biopsied under US guidance.

RESULTS

56/233 FAs were positive at biopsy. The subjective score significantly predicted biopsy results (P < 0.01). As compared to SS(1) FAs, the odds ratios (OR) of malignancy of SS(2) and SS(3) FAs were 9.9 (1.8-55.9) and 163.8 (11.5-2331). Unlike FAs' shape, a simple combination of MR signal abnormalities (into "low-risk", "intermediate" and "high-risk" groups) significantly predicted biopsy results (P < 0.008). As compared to "low risk" FAs, the OR of malignancy of "intermediate" and "high-risk" FAs were 4.5 (1.1-18.4) and 52.7 (6.8-407) in the overall population and 5.4 (1.1-27.2) and 118.2 (6.1-2301) in PZ.

CONCLUSIONS

A simple combination of signal abnormalities of individual MR sequences can significantly stratify the risk of malignancy of FAs, holding promise of a more standardised interpretation of MRI by readers with varying experience.

KEY POINTS

• Using multiparameter(mp)-MRI, experienced uroradiologists can stratify the malignancy risk of prostatic lesions • The shape of prostatic focal abnormalities in the peripheral zone does not help predicting malignancy. • A simple combination of findings at mp-MRI can help less-experienced radiologists.

Documenting the location of prostate biopsies with image fusion

OBJECTIVE To develop a system that documents the location of transrectal ultrasonography (TRUS)-guided prostate biopsies by fusing them to MRI scans obtained prior to biopsy, as the actual location of prostate biopsies is rarely known. PATIENTS AND METHODS Fifty patients (median age 61) with a median prostate-specific antigen (PSA) of 5.8 ng/ml underwent 3T endorectal coil MRI prior to biopsy. 3D TRUS images were obtained just prior to standard TRUS-guided 12-core sextant biopsies wherein an electromagnetic positioning device was attached to the needle guide and TRUS probe in order to track the position of each needle pass. The 3D-TRUS image documenting the location of each biopsy was fused electronically to the T2-weighted MRI. Each biopsy needle track was marked on the TRUS images and these were then transposed onto the MRI. Each biopsy site was classified pathologically as positive or negative for cancer and the Gleason score was determined. RESULTS The location of all (n= 605) needle biopsy tracks was successfully documented on the T2-weighted (T2W) MRI. Among 50 patients, 20 had 56 positive cores. At the sites of biopsy, T2W signal was considered 'positive' for cancer (i.e. low in signal intensity) in 34 of 56 sites. CONCLUSION It is feasible to document the location of TRUS-guided prostate biopsies on pre-procedure MRI by fusing the pre-procedure TRUS to an endorectal coil MRI using electromagnetic needle tracking. This procedure may be useful in documenting the location of prior biopsies, improving quality control and thereby avoiding under-sampling of the prostate as well as directing subsequent biopsies to regions of the prostate not previously sampled.