Current status of MRI for the diagnosis, staging and prognosis of prostate cancer: implications for focal therapy and active surveillance

A phase and frequency alignment protocol for 1H MRSI data of the prostate

(1)H MRSI of the prostate reveals relative metabolite levels that vary according to the presence or absence of tumour, providing a sensitive method for the identification of patients with cancer. Current interpretations of prostate data rely on quantification algorithms that fit model metabolite resonances to individual voxel spectra and calculate relative levels of metabolites, such as choline, creatine, citrate and polyamines. Statistical pattern recognition techniques can potentially improve the detection of prostate cancer, but these analyses are hampered by artefacts and sources of noise in the data, such as variations in phase and frequency of resonances. Phase and frequency variations may arise as a result of spatial field gradients or local physiological conditions affecting the frequency of resonances, in particular those of citrate. Thus, there are unique challenges in developing a peak alignment algorithm for these data. We have developed a frequency and phase correction algorithm for automatic alignment of the resonances in prostate MRSI spectra. We demonstrate, with a simulated dataset, that alignment can be achieved to a phase standard deviation of 0.095  rad and a frequency standard deviation of 0.68  Hz for the citrate resonances. Three parameters were used to assess the improvement in peak alignment in the MRSI data of five patients: the percentage of variance in all MRSI spectra explained by their first principal component; the signal-to-noise ratio of a spectrum formed by taking the median value of the entire set at each spectral point; and the mean cross-correlation between all pairs of spectra. These parameters showed a greater similarity between spectra in all five datasets and the simulated data, demonstrating improved alignment for phase and frequency in these spectra. This peak alignment program is expected to improve pattern recognition significantly, enabling accurate detection and localisation of prostate cancer with MRSI.

Focal therapy in the management of prostate cancer: an emerging approach for localized prostate cancer

A widespread screening with prostate-specific antigen (PSA) has led increased diagnosis of localized prostate cancer along with a reduction in the proportion of advanced-stage disease at diagnosis. Over the past decade, interest in focal therapy as a less morbid option for the treatment of localized low-risk prostate cancer has recently been renewed due to downward stage migration. Focal therapy stands midway between active surveillance and radical treatments, combining minimal morbidity with cancer control. Several techniques of focal therapy have potential for isolated ablation of a tumor focus with sparing of uninvolved surround tissue demonstrating excellent short-term cancer control and a favorable patient's quality of life. However, to date, tissue ablation has mostly used for near-whole prostate gland ablation without taking advantage of accompanying the technological capabilities. The available ablative technologies include cryotherapy, high-intensity focused ultrasound (HIFU), and vascular-targeted photodynamic therapy (VTP). Despite the interest in focal therapy, this technology has not yet been a well-established procedure nor provided sufficient data, because of the lack of randomized trial comparing the efficacy and morbidity of the standard treatment options. In this paper we briefly summarize the recent data regarding focal therapy for prostate cancer and these new therapeutic modalities.

Imaging of prostate cancer: a platform for 3D co-registration of in-vivo MRI ex-vivo MRI and pathology

OBJECTIVES

Multi-parametric MRI is emerging as a promising method for prostate cancer diagnosis. prognosis and treatment planning. However, the localization of in-vivo detected lesions and pathologic sites of cancer remains a significant challenge. To overcome this limitation we have developed and tested a system for co-registration of in-vivo MRI, ex-vivo MRI and histology.

MATERIALS AND METHODS

Three men diagnosed with localized prostate cancer (ages 54-72, PSA levels 5.1-7.7 ng/ml) were prospectively enrolled in this study. All patients underwent 3T multi-parametric MRI that included T2W, DCE-MRI, and DWI prior to robotic-assisted prostatectomy. Ex-vivo multi-parametric MRI was performed on fresh prostate specimen. Excised prostates were then sliced at regular intervals and photographed both before and after fixation. Slices were perpendicular to the main axis of the posterior capsule, i.e., along the direction of the rectal wall. Guided by the location of the urethra, 2D digital images were assembled into 3D models. Cancer foci, extra-capsular extensions and zonal margins were delineated by the pathologist and included in 3D histology data. A locally-developed software was applied to register in-vivo, ex-vivo and histology using an over-determined set of anatomical landmarks placed in anterior fibro-muscular stroma, central. transition and peripheral zones. The mean root square distance across corresponding control points was used to assess co-registration error.

RESULTS

Two specimens were pT3a and one pT2b (negative margin) at pathology. The software successfully fused in-vivo MRI. ex-vivo MRI fresh specimen and histology using appropriate (rigid and affine) transformation models with mean square error of 1.59 mm. Coregistration accuracy was confirmed by multi-modality viewing using operator-guided variable transparency.

CONCLUSION

The method enables successful co-registration of pre-operative MRI, ex-vivo MRI and pathology and it provides initial evidence of feasibility of MRI-guided surgical planning.

ESUR prostate MR guidelines 2012

The aim was to develop clinical guidelines for multi-parametric MRI of the prostate by a group of prostate MRI experts from the European Society of Urogenital Radiology (ESUR), based on literature evidence and consensus expert opinion. True evidence-based guidelines could not be formulated, but a compromise, reflected by “minimal” and “optimal” requirements has been made. The scope of these ESUR guidelines is to promulgate high quality MRI in acquisition and evaluation with the correct indications for prostate cancer across the whole of Europe and eventually outside Europe. The guidelines for the optimal technique and three protocols for “detection”, “staging” and “node and bone” are presented. The use of endorectal coil vs. pelvic phased array coil and 1.5 vs. 3 T is discussed. Clinical indications and a PI-RADS classification for structured reporting are presented.

Key Points

• This report provides guidelines for magnetic resonance imaging (MRI) in prostate cancer.

• Clinical indications, and minimal and optimal imaging acquisition protocols are provided.

• A structured reporting system (PI-RADS) is described.

Focal therapy for prostate cancer: patient selection and evaluation

Recent stage migration toward low-risk prostate cancer, overtreatment of biologically insignificant tumors with radical prostatectomy at the additional expense of a non-negligible morbidity and undertreatment of patients improperly selected for active surveillance are the main reasons that have fueled the concept of focal therapy. Optimal selection of patients is the key for the successful implementation of focal therapy. Selection criteria for focal therapy vary widely and depend on clinical, histological and imaging characteristics of the patients that are highlighted in this article. In addition, the rationales, merits and limitations of the available methods for the assessment of potential candidates, the evaluation of treatment efficacy and follow-up of these patients are discussed.

[Diagnose importance of multiparametric magnetic resonance tomography for prostate cancer]

Prostate cancer is biologically and clinically a heterogeneous disease which makes imaging evaluation challenging. Magnetic resonance imaging (MRI) has considerable potential to improve prostate cancer detection and characterization. Until recently morphologic MRI has not been routinely incorporated into clinical care because of its limitation to detect, localize and characterize prostate cancer. Performing prostate gland MRI using functional techniques has the potential to provide unique information regarding tumor behavior, including treatment response. In order for multiparametric MRI data to have an impact on patient management, the collected data need to be relayed to clinicians in a standardized way for image construction, analysis and interpretation. This will ensure that patients are treated effectively and in the most appropriate way. Scoring systems similar to those employed successfully for breast imaging need to be developed.

Focal therapy for prostate cancer - where are we in 2011?

Prostate cancer treatment is a controversial topic amongst physicians and patients alike. Radical therapies such as prostatectomy and whole gland radiation offer the best outcomes in terms of oncologic efficacy, but the decision to undergo treatment must be weighed against its potential morbidity. Over the past decade, the concept of focal therapy for prostate cancer has been introduced as a potential method of achieving oncologic control with a lesser degree of morbidity. Focal therapy refers to isolated ablation of a tumor focus with sparing of uninvolved, surrounding tissue. While it remains in the early stages of development, considerable research is underway that will help determine the optimal method of achieving this goal. Current areas of investigation include appropriate candidate selection, lesion identification, modality of treatment, and follow-up strategies.

Engineered multifunctional nanocarriers for cancer diagnosis and therapeutics

This article reviews advances in the design and development of multifunctional carbon-based and/or magnetic nanoparticle systems (or simply 'nanocarriers') for early cancer diagnosis and spatially and temporally controlled therapy. The critical issues in cancer diagnosis and treatment are addressed based on novel nanotechnologies such as real-time in-vivo imaging, drug storage and release, and specific cancer-cell targeting. The implementation of nanocarriers into animal models and the subsequent effectiveness in treating tumors is also reviewed. Recommendations for future research are given.

Combined multiparametric MRI and targeted biopsies improve anterior prostate cancer detection, staging, and grading

OBJECTIVES

To assess the efficacy of magnetic resonance imaging (MRI) in detection of suspicious anterior prostate lesions, and its role in staging and grading of anterior prostate cancer (APC).

METHODS

Between January 2008 and August 2009, 243 patients had prostate cancer diagnosed at 12-cores posterior systematic biopsies and additional 2-cores transrectal ultrasound-guided, free-hand-targeted biopsy at any area suspicious for malignancy at prebiopsy multiparametric MRI. We conducted a retrospective study of 45 of 243 (19%) patients with an area suspicious for malignancy at MRI predominantly located in the anterior part of the gland, for which targeted biopsies were positive. Targeted vs systematic biopsy cancer detection rate and upgrading based on length of cancer in the most involved core and Gleason score were measured.

RESULTS

Of the 45 patients, 46 separate APCs were identified at MRI with positive targeted biopsies. APC was not detected by systematic biopsies in 21 (46%) cases and detected in 25 (54%) cases. For these 25 cases, median cancer length of the most involved core in targeted compared with systematic biopsies was 8 mm vs 1 mm (P <.001), respectively. Significant Gleason score upgrading was observed in 11 of 25 (44%) cases. Correlation coefficient between the cancer length on targeted biopsies and the antero-posterior diameter of the area suspicious for malignancy on MRI was r(2) = .6 (P <.001). Separate posterior cancer was diagnosed in 26 patients.

CONCLUSIONS

Targeted biopsies based on a prebiopsy MRI-detected lesion improved detection rate, volume, and grade of APC compared with currently used 12-cores systematic biopsies.

Role of magnetic resonance imaging before initial biopsy: comparison of magnetic resonance imaging-targeted and systematic biopsy for significant prostate cancer detection

OBJECTIVE

•To compare magnetic resonance imaging (MRI)-targeted biopsies with extended systematic biopsies for the detection of significant prostate cancer.

METHODS

•In all, 555 consecutive patients with suspicion of prostate cancer had pre-biopsy dynamic contrast-enhanced 1.5-tesla (T) MRI with pelvic coil, 10-12 transrectal ultrasound-guided extended systematic biopsies plus two targeted biopsies at any MRI area suspicious for malignancy. •Significant prostate cancer was defined as >5 mm total cancer length and/or any Gleason pattern >3. •Cancer length and grade at biopsy were reported and located on a 24-sector map.

RESULTS

•Median (range) prostate-specific antigen (PSA) was 6.75 (0.18-100) ng/mL. •MRI was positive in 351 (63%) patients and, overall, 302 (54%) had cancer at extended systematic biopsies and/or targeted biopsies. Of 302 cancers detected, 249 (82%) were significant prostate cancers and 53 (18%) were nonsignificant prostate cancers. •Extended systematic biopsies did not detect 12 significant prostate cancers and targeted biopsies did not detect 13 significant prostate cancers. For significant prostate cancer detection, sensitivity, specificity and accuracy of targeted biopsies were 0.95, 1.0 and 0.98. The values for extended systematic biopsies were 0.95, 0.83, and 0.88. •The detection accuracy of significant prostate cancer by targeted biopsies was higher than that by extended systematic biopsies (P < 0.001). Targeted biopsies also detected 16% more grade 4/5 cases and better quantified the cancer than extended systematic biopsies, with cancer length of 5.56 vs. 4.70 mm (P= 0.002). • A targeted biopsies-only strategy without extended systematic biopsies would have necessitated a mean of 3.8 cores performed in only 63% of patients with positive MRI and avoided the potentially unnecessary diagnosis of 13% (53/302) of nonsignificant prostate cancers.

CONCLUSIONS

• Strategy of targeted biopsies alone at pre-biopsy MRI-suspicious areas is an attractive potential alternative to extended systematic biopsies for detection of significant prostate cancer. •Further studies are necessary to validate the strategy of targeted biopsies alone.

Magnetic resonance imaging for the detection, localisation, and characterisation of prostate cancer: recommendations from a European consensus meeting

BACKGROUND

Multiparametric magnetic resonance imaging (mpMRI) may have a role in detecting clinically significant prostate cancer in men with raised serum prostate-specific antigen levels. Variations in technique and the interpretation of images have contributed to inconsistency in its reported performance characteristics.

OBJECTIVE

Our aim was to make recommendations on a standardised method for the conduct, interpretation, and reporting of prostate mpMRI for prostate cancer detection and localisation.

DESIGN, SETTING, AND PARTICIPANTS

A consensus meeting of 16 European prostate cancer experts was held that followed the UCLA-RAND Appropriateness Method and facilitated by an independent chair.

MEASUREMENT

Before the meeting, 520 items were scored for "appropriateness" by panel members, discussed face to face, and rescored.

RESULTS AND LIMITATIONS

Agreement was reached in 67% of 260 items related to imaging sequence parameters. T2-weighted, dynamic contrast-enhanced, and diffusion-weighted MRI were the key sequences incorporated into the minimum requirements. Consensus was also reached on 54% of 260 items related to image interpretation and reporting, including features of malignancy on individual sequences. A 5-point scale was agreed on for communicating the probability of malignancy, with a minimum of 16 prostatic regions of interest, to include a pictorial representation of suspicious foci. Limitations relate to consensus methodology. Dominant personalities are known to affect the opinions of the group and were countered by a neutral chairperson.

CONCLUSIONS

Consensus was reached on a number of areas related to the conduct, interpretation, and reporting of mpMRI for the detection, localisation, and characterisation of prostate cancer. Before optimal dissemination of this technology, these outcomes will require formal validation in prospective trials.

Focal therapy for prostate cancer: fact or fiction?

Prostate cancer is the commonest male cancer diagnosed in men in the UK, and the treatment of organ confined prostate cancer is a subject of much debate. Focal therapy for prostate cancer intends to treat the cancer within the prostate, whilst sparing the majority of the benign prostate tissue. In addition, the intention is to avoid treatment effects in the surrounding structures, the damage of which leads to the side effects commonly associated with radical whole gland therapies. This relies on accurate localization of the prostate cancer by biopsy and imaging followed by treatment using a modality capable of delivery to a focal area within the prostate. Focal therapy lies between the current extremes of radical whole gland treatment and active surveillance. There have been many articles reviewing the concept of focal therapy for organ confined prostate cancer, but with a paucity of data available for analysis. This is being addressed with an increase in the published data on focal therapy, using a number of different modalities. In this review, we address the question of whether the data currently published does in fact support the further development of the focal therapy approach, or whether it is a concept best relegated to the realms of fiction.

MR to ultrasound registration for image-guided prostate interventions

A deformable registration method is described that enables automatic alignment of magnetic resonance (MR) and 3D transrectal ultrasound (TRUS) images of the prostate gland. The method employs a novel "model-to-image" registration approach in which a deformable model of the gland surface, derived from an MR image, is registered automatically to a TRUS volume by maximising the likelihood of a particular model shape given a voxel-intensity-based feature that represents an estimate of surface normal vectors at the boundary of the gland. The deformation of the surface model is constrained by a patient-specific statistical model of gland deformation, which is trained using data provided by biomechanical simulations. Each simulation predicts the motion of a volumetric finite element mesh due to the random placement of a TRUS probe in the rectum. The use of biomechanical modelling in this way also allows a dense displacement field to be calculated within the prostate, which is then used to non-rigidly warp the MR image to match the TRUS image. Using data acquired from eight patients, and anatomical landmarks to quantify the registration accuracy, the median final RMS target registration error after performing 100 MR-TRUS registrations for each patient was 2.40 mm.

[Active surveillance for prostate cancer: usefulness of endorectal MR at 1.5 Tesla with pelvic phased array coil in detecting significant tumors]

PURPOSE

To describe and assess MRI signs of significant tumor in a series of patients who all underwent radical prostatectomy and also fulfilled criteria to choose active surveillance according to French "SurAcaP" protocol.

PATIENTS AND METHODS

The clinical reports of 681 consecutive patients operated on for prostate cancer between 2002 and 2007 were reviewed retrospectively. All patients had endorectal MR (1.5 Tesla) with pelvic phased array coil. (1.5 T erMR PPA). Sixty-one patients (8.9%) fulfilled "SurAcaP" protocol criteria. Preoperative data (MR+core biopsy) were assessed by comparison to whole-mount step section pathology.

RESULTS

85.3% of the 61 patients entering SurAcaP protocol had significant tumor at pathology. (Non Organ Confined Disease (Non OCD)=8.2%, Gleason sum score>6=39.2%). A new exclusion criterion has been assessed: T3MRI±NPS>1 as a predictor tool of significant tumor. ("T3MRI±NPS>1"=Non OCD at MR±number of positive sextants involved in tumor at MR and/or Core Biopsy > to 1). Sensitivity, specificity, PPV, NPV of the criterion "T3MRI±NPS>1" in predicting significant tumor were, respectively: 77%, 33%, 86%, 20%. Adding this criterion to other criteria of the "SurAcaP" protocol could allow the exclusion of all Non OCD, and a decrease in Gleason sum Score>6 rates (20%).

CONCLUSION

Endorectal MR at 1.5 Tesla with pelvic-phased array coil should be considered when selecting patients for active surveillance in the management of prostate cancer. A criterion based upon MR and core biopsy findings, called "T3MR±NSP>1" may represent an exclusion citeria due to its ability to predict significant tumor.

Update on prostate imaging

Successful and accurate imaging of prostate cancer is integral to its clinical management from detection and staging to subsequent monitoring. Various modalities are used including ultrasound, computed tomography, and magnetic resonance imaging, with the greatest advances seen in the field of magnetic resonance.

Recent advances in focal therapy of prostate and kidney cancer

The concept of focal therapy in oncologic surgery refers to maximizing healthy tissue preservation while maintaining excellent cancer control outcomes. Herein, we address the recent advantages in the field of focal therapy for both kidney and prostate cancer, focusing on technological achievements and future perspectives.