The role of magnetic resonance imaging (MRI) in focal therapy for prostate cancer: recommendations from a consensus panel

In-bore MRI interventions: current status and future applications

PURPOSE OF REVIEW

This review discusses the feasibility, recent advances and current status of in-bore MRI-guided interventional techniques for diagnosis and treatment of focal prostate cancer (PCa) and also explores the future applications, highlighting the emerging strategies for the treatment of PCa.

RECENT FINDINGS

Multiparametric MRI has opened up opportunities for diagnosis and targeted therapeutics to the site of disease within the organ wherein minimizing the incidence of treatment-related toxicity of whole gland therapy. MRI-guided targeted biopsy has a higher detection rate for significant cancer and lower rate of detection of insignificant cancer. In comparison to ultrasound-guided focal therapy, in-bore treatment provides the advantage of real time thermal monitoring during treatment and assessment of treatment coverage by an enhanced scan immediately post-treatment. Preliminary results of ongoing phase I and II in-bore focal PCa treatment trials via transperineal, transrectal and transurethral routes, using different energy modalities for the ablation, have shown promising results.

SUMMARY

Advances in multiparametric-MRI has opened up opportunities for in-bore targeted focal treatment of PCa in the correctly selected patient.

Partial Gland Ablation for Prostate Cancer: Report of a Food and Drug Administration, American Urological Association, and Society of Urologic Oncology Public Workshop

OBJECTIVE

To summarize the discussion that took place at a public workshop, co-sponsored by the U.S. Food and Drug Administration, the American Urological Association, and Society of Urologic Oncology reviewing the current state of the art for partial gland ablation (PGA) for the management of patients with prostate cancer. The purpose of this workshop was to discuss potential indications, current available evidence, and designs for future trials to provide the evidence needed by patients and providers to decide how and when to use PGA.

METHODS

A workshop evaluating PGA for prostate cancer was held in New Orleans, Louisiana, in May 2015. Invited experts representing all stakeholders and attendees discussed the regulatory development of medical products, technology available, potential indications, and designs of trials to evaluate this modality of therapy.

RESULTS

The panel presented the current information on the technologies available to perform PGA, the potential indications, and results of prior consensus conferences. Use of magnetic resonance imaging for patient selection, guide therapy, and follow-up was discussed. Designs of trials to assess PGA outcomes were discussed.

CONCLUSION

The general consensus was that currently available technologies are capable of selective ablation with reasonable accuracy, but that criteria for patient selection remain debatable, and long-term cancer control remains to be established in properly designed and well-performed prospective clinical trials. Concerns include the potential for excessive, unnecessary use in patients with low-risk cancer and, conversely, that current diagnostic techniques may underestimate the extent and aggressiveness of some cancers, leading to inadequate treatment.

Magnetic resonance imaging for prostate cancer: Comparative studies including radical prostatectomy specimens and template transperineal biopsy

Purpose

Multiparametric magnetic resonance imaging (mpMRI) is an emerging technique aiming to improve upon the diagnostic sensitivity of prostate biopsy. Because of variance in interpretation and application of techniques, results may vary. There is likely a learning curve to establish consistent reporting of mpMRI. This study aims to review current literature supporting the diagnostic utility of mpMRI when compared with radical prostatectomy (RP) and template transperineal biopsy (TTPB) specimens.

Methods

MEDLINE and PubMed database searches were conducted identifying relevant literature related to comparison of mpMRI with RP or TTPB histology.

Results

Data suggest that compared with RP and TTPB specimens, the sensitivity of mpMRI for prostate cancer (PCa) detection is 80–90% and the specificity for suspicious lesions is between 50% and 90%.

Conclusions

mpMRI has an increasing role for PCa diagnosis, staging, and directing management toward improving patient outcomes. Its sensitivity and specificity when compared with RP and TTPB specimens are less than what some expect, possibly reflecting a learning curve for the technique of mpMRI.

Pitfalls in Interpreting mp-MRI of the Prostate: A Pictorial Review with Pathologic Correlation

Objectives

The purpose of this pictorial review is to present a wide spectrum of prostate multiparametric MRI (mp-MRI) pitfalls that may occur in clinical practice, with radiological and pathological correlation.

Methods

All examinations were performed according to ESUR Guidelines protocols.

Results and Conclusion

mp-MRI imaging of the prostate often leads to interpreting doubts and misdiagnosis due to the many interpretative pitfalls that a tissue, whether healthy or treated, may cause. These “false-positive” findings may occur in each stage of the disease history, from the primary diagnosis and staging, to the post-treatment stage, and whether they are caused by the tissue itself or are iatrogenic, their recognition is critical for proper treatment and management. Knowledge of these known pitfalls and their interpretation in the anatomical-radiological context can help radiologists avoid misdiagnosis and consequently mistreatment.

Main Messages

• Some physiological changes in the peripheral and central zone may simulate prostate cancer.

• Technical errors, such as mispositioned endorectal coils, can affect the mp-MRI interpretation.

• Physiological changes post-treatment can simulate recurrence

MRI-guided biopsies and minimally invasive therapy for prostate cancer

Recent advances in multiparametric magnetic resonance imaging (mp-MRI) have led to a paradigm shift in the diagnosis and management of prostate cancer (PCa). Its sensitivity in detecting clinically significant cancer and the ability to localize the tumor within the prostate gland has opened up discussion on targeted diagnosis and therapy in PCa. Use of mp-MRI in conjunction with prostate-specific antigen followed by targeted biopsy allows for a better diagnostic pathway than transrectal ultrasound (TRUS) biopsy and improves the diagnosis of PCa. Improved detection of PCa by mp-MRI has also opened up opportunities for focal therapy within the organ while reducing the incidence of side-effects associated with the radical treatment methods for PCa. This review discusses the evidence and techniques for in-bore MRI-guided prostate biopsy and provides an update on the status of MRI-guided targeted focal therapy in PCa.

Dose painting to treat single-lobe prostate cancer with hypofractionated high-dose radiation using targeted external beam radiation: Is it feasible?

Targeted focal therapy strategies for treating single-lobe prostate cancer are under investigation. In this planning study, we investigate the feasibility of treating a portion of the prostate to full-dose external beam radiation with reduced dose to the opposite lobe, compared with full-dose radiation delivered to the entire gland using hypofractionated radiation. For 10 consecutive patients with low- to intermediate-risk prostate cancer, 2 hypofractionated, single-arc volumetric-modulated arc therapy (VMAT) plans were designed. The first plan (standard hypofractionation regimen [STD]) included the entire prostate gland, treated to 70 Gy delivered in 28 fractions. The second dose painting plan (DP) encompassed the involved lobe treated to 70 Gy delivered in 28 fractions, whereas the opposing, uninvolved lobe received 50.4 Gy in 28 fractions. Mean dose to the opposing neurovascular bundle (NVB) was considerably lower for DP vs STD, with a mean dose of 53.9 vs 72.3 Gy (p < 0.001). Mean penile bulb dose was 18.6 Gy for DP vs 19.2 Gy for STD (p = 0.880). Mean rectal dose was 21.0 Gy for DP vs 22.8 Gy for STD (p = 0.356). Rectum V70 (the volume receiving ≥70 Gy) was 2.01% for DP vs 2.74% for STD (p = 0.328). Bladder V70 was 1.69% for DP vs 2.78% for STD (p = 0.232). Planning target volume (PTV) maximum dose points were 76.5 and 76.3 Gy for DP and STD, respectively (p = 0.760). This study demonstrates the feasibility of using VMAT for partial-lobe prostate radiation in patients with prostate cancer involving 1 lobe. Partial-lobe prostate plans appeared to spare adjacent critical structures including the opposite NVB.

Focal therapy for prostate cancer: The current status

Purpose

In an era of increasing prostate cancer incidence and earlier detection, the assessment of clinical significance of prostate cancer is critical. Minimally invasive therapies are increasingly being investigated in localized prostate cancer.

Methods and results

In this review, we discuss the current status of magnetic resonance imaging targeted fusion prostate biopsy and focal therapy for prostate cancer, its rationale, and techniques.

Conclusion

Focal therapy offers a promising outlook for prostate cancer treatment, with the goal of effectively achieving cancer control while minimizing morbidity. Long term studies are needed.

Can we deliver randomized trials of focal therapy in prostate cancer?

Tissue-preserving focal therapies, such as brachytherapy, cryotherapy, high-intensity focused ultrasound and photodynamic therapy, aim to target individual cancer lesions rather than the whole prostate. These treatments have emerged as potential interventions for localized prostate cancer to reduce treatment-related adverse-effects associated with whole-gland treatments, such as radical prostatectomy and radiotherapy. In this article, the Prostate Cancer RCT Consensus Group propose that a novel cohort-embedded randomized controlled trial (RCT) would provide a means to study men with clinically significant localized disease, which we defined on the basis of PSA level (≤ 15 ng/ml or ≤ 20 ng/ml), Gleason grade (Gleason pattern ≤ 4 + 4 or ≤ 4 + 3) and stage (≤ cT2cN0M0). This RCT should recruit men who stand to benefit from treatment, with the control arm being whole-gland surgery or radiotherapy. Composite outcomes measuring rates of local and systemic salvage therapies at 3-5 years might best constitute the basis of the primary outcome on which to change practice.

Multiparametric MRI identifies and stratifies prostate cancer lesions: implications for targeting intraprostatic targets

PURPOSE

To assess the ability of multiparametric (mp) MRI (mp-MRI) to identify, stratify, and localize biopsy-proven prostate cancer lesions in a risk-stratified patient population.

METHODS AND MATERIALS

We retrospectively analyzed 57 patients who had mp-MRI and core needle biopsy during diagnostic prostate cancer evaluation. The MRI sequences were scored for suspicion of cancer with a previously described system. Distributions of mp-MRI scores were compared across National Comprehensive Cancer Network prostate cancer risk groups. The mp-MRI-identified lesions were compared with the location of positive core needle biopsies to assess mp-MRI localization of true lesions.

RESULTS

The mp-MRI scoring system identified lesions in 84% (48/57) of the patients, including 100% (12/12) in the high-risk group. Scores assigned to lesions in patients in intermediate- and high-risk groups were statistically higher than those in the low-risk group, with a relative risk of 6.72 (95% confidence interval: 2.32-19.51, p<0.001) of having an aggressive score assigned in high-risk patients compared with the low-risk patients. In comparing the localization data from core needle biopsy, 68% of the patients had an MRI-identified lesion in or within one adjacent sextant of the same prostate hemigland, including 85% of aggressive lesions.

CONCLUSIONS

Use of mp-MRI at the time of diagnosis can identify intraprostatic lesions and assign suspicion for high-risk disease. These data show that high-risk patients are more likely to have suspicious imaging-identified lesions that correlate to the location of biopsy-proven prostate cancer. At this time, the use of mp-MRI to define focal targets represents a complementary tool to patient evaluation for focal therapy strategies.

Current Ability of Multiparametric Prostate Magnetic Resonance Imaging and Targeted Biopsy to Improve the Detection of Prostate Cancer

INTRODUCTION

Recent advancements in imaging technology have significantly increased the diagnostic accuracy of magnetic resonance imaging for prostate cancer. However, tissue diagnosis and grading remain the gold standard for diagnosis and prognostication. Because transrectal ultrasound guided prostate biopsy performs poorly, extensive research has been conducted into biopsy techniques that are guided by magnetic resonance imaging, including direct in-bore, cognitive fusion and magnetic resonance imaging/ultrasound fusion guided biopsies.

METHODS

The PubMed® database was searched from inception until January 15, 2014 for criteria pertaining to targeted prostate biopsy.

RESULTS

Initial studies of the 3 types of targeted prostate biopsy yielded similar results. Most importantly, targeted biopsy detects a greater amount of clinically significant prostate cancer than does transrectal ultrasound guided biopsy. Magnetic resonance imaging/ultrasound fusion guided biopsy has generated the most interest, as it is an office based procedure that does not require a significant change from the current workflow of transrectal prostate biopsy. These techniques hold great promise in the areas of patient selection for definitive treatment, appropriate screening, active surveillance and focal therapy for prostate cancer.

CONCLUSIONS

Targeted prostate biopsy has the potential to significantly improve the way patients are screened, treated and monitored in the setting of prostate cancer. These techniques allow for an individualized approach to each patient, which is a substantial improvement over the current practice of effectively random prostate biopsies. Large, multicenter studies are necessary to determine whether targeted prostate biopsy will become a definitive standard of care.