Gadolinium-enhanced MRI in the evaluation of minimally invasive treatments of the prostate: correlation with histopathologic findings

Real-Time and Delayed Imaging of Tissue and Effects of Prostate Tissue Ablation

PURPOSE OF REVIEW

Prostate ablation is increasingly being utilized for the management of localized prostate cancer. There are several energy modalities with varying mechanism of actions which are currently used for prostate ablation. Prostate ablations, whether focal or whole gland, are performed under ultrasound and/or MRI guidance for appropriate treatment plan execution and monitoring. A familiarity with different intraoperative imaging findings and expected tissue response to these ablative modalities is paramount. In this review, we discuss the intraoperative, early, and delayed imaging findings in prostate from the effects of prostate ablation.

RECENT FINDINGS

The monitoring of ablation both during and after the therapy became increasingly important due to the precise targeting of the target tissue. Recent findings suggest that real-time imaging techniques such as MRI or ultrasound can provide anatomical and functional information, allowing for precise ablation of the targeted tissue and increasing the effectiveness and precision of prostate cancer treatment. While intraprocedural imaging findings are variable, the follow-up imaging demonstrates similar findings across various energy modalities. MRI and ultrasound are two of the frequently used imaging techniques for intraoperative monitoring and temperature mapping of important surrounding structures. Follow-up imaging can provide valuable information about ablated tissue, including the success of the ablation, presence of residual cancer or recurrence after the ablation. It is critical and helpful to understand the imaging findings during the procedure and at different follow-up time periods to evaluate the procedure and its outcome.

Rezūm System Water Vapor Treatment for Lower Urinary Tract Symptoms/Benign Prostatic Hyperplasia: Validation of Convective Thermal Energy Transfer and Characterization With Magnetic Resonance Imaging and 3-Dimensional Renderings

OBJECTIVE

To evaluate by magnetic resonance imaging the physical effects of convective thermal energy transfer with water vapor as a means of treating lower urinary tract symptoms due to benign prostatic hyperplasia.

METHODS

Sixty-five men with lower urinary tract symptoms were treated with the Rezūm System by transurethral intraprostatic injection of water vapor. A group of 45 of these men consented to undergo a series of gadolinium-enhanced magnetic resonance imagings of the prostate after treatment to monitor the size and location of ablative lesions, their time course of resolution, and the corresponding change in prostate tissue volume. Visualization was conducted at 1 week, 1, 3, and 6 months after treatment.

RESULTS

Outcomes were available for 44 patients. Convective thermal lesions were limited to the transition zone and correlated with targeted treatment locations. At 1 week after treatment, the mean volume of ablative lesions was 8.2 cm(3) (0.5-24.0 cm(3)). At 6 months, whole prostate volume was reduced by a mean of 28.9% and transition zone volume by 38.0% as compared with baseline 1-week images. At 3 and 6 months after treatment, the lesion volumes had reduced by 91.5% and 95.1%, respectively. Lesions remained within the targeted treatment zone without compromising integrity of the bladder, rectum, or striated urinary sphincter.

CONCLUSION

This imaging study confirms the delivery of convective water vapor technology to create thermal lesions in the prostate tissue. Lesions generated underwent near complete resolution by 3 and 6 months after treatment with a concomitant one-third reduction in overall prostate and transition zone volumes.

Transurethral convective water vapor as a treatment for lower urinary tract symptomatology due to benign prostatic hyperplasia using the Rezūm(®) system: evaluation of acute ablative capabilities in the human prostate

Background

The purpose of this study was to assess the acute ablative characteristics of transurethral convective water vapor (steam) using the Rezūm^® system in men with benign prostatic hyperplasia through histologic and radiographic studies.

Methods

Seven patients were treated with transurethral intraprostatic injections of sterile steam under endoscopic visualization followed by previously scheduled adenectomies. The extirpated adenomas were grossly examined followed by whole mount sectioning and staining with triphenyl-tetrazolium chloride (TTC) to evaluate thermal ablation. Histology was performed after hematoxylin and eosin staining on one prostate. After review of results from the first patient cohort, an additional 15 patients with clinical benign prostatic hyperplasia were treated followed by gadolinium-enhanced magnetic resonance imaging (MRI) at one week.

Results

In the first patient cohort, gross examination of TTC-stained tissue showed thermal ablation in the transition zone. In addition, there was a distinct interface between viable and necrotic prostatic parenchyma. Histopathologic examination revealed TTC staining-outlined necrotic versus viable tissue. Gadolinium-enhanced MRIs in the cohort of 15 patients demonstrated lesion defects in all patients at 1 week post-procedure. Coalesced lesions were noted with a mean (± standard deviation) lesion volume of 9.6±8.5 cm³. The largest lesion volume was 35.1 cm³. Ablation using vapor was rapid and remained confined to the transition zone, consistent with the thermodynamic principles of convective thermal energy transfer.

Conclusion

Thermal ablation was observed in all specimens. The resulting coalescing ablative lesions, as seen on MRI, were confined to the transition zone. These studies confirm the ablative capabilities of vapor, validate the thermodynamic principles of convective heating, and allow for further clinical studies.

Early experience in MRI-guided therapies of prostate cancer: HIFU, laser and photodynamic treatment

Prostate cancer screening has resulted in earlier diagnosis with lower-grade disease, leading to over-detection and over-treatment in a significant number of patients. Current whole-gland radical treatments are associated with significant rates of morbidity. The high prevalence of low-risk disease together with an inability to accurately identify those men harboring more aggressive cancers has led to tremendous research in low-morbidity focal therapies for prostate cancer. This review summarizes the early experiences with focal therapy with emphasis on early applications of laser, high-intensity focuses ultrasound, and photodynamic approaches.

Evolution from active surveillance to focal therapy in the management of prostate cancer

Organ-preserving therapies are widely accepted in many facets of medicine and, more recently, in oncology. For example, partial nephrectomy is now accepted as a preferred alternative over radical nephrectomy for small (up to 4 cm or T1) tumors. Focal therapy (FT) is another organ-preserving strategy applying energy (cryotherapy, laser ablation and/or high-intensity focused ultrasound) to destroy tumors while leaving the majority of the organ, surrounding tissue and structures unscathed and functional. Owing to the perceived multifocality of prostate cancer (PCa) technology limitations, in the past PCa was not considered suitable for FT. However, with the rise of active surveillance for the management of low-risk PCa in carefully selected patients, FT is emerging as an alternative. This is owing to technology improvements in imaging and energy-delivery systems to ablate tissue, as well as the realization that many men and clinicians still desire tumor control. With the postulated ability to ablate tumors with minimal morbidity, FT may have found a role in the management of PCa; the aim of FT a being long-term cancer control without the morbidity associated with radical therapies. Data for FT in PCa have been derived from case series and small Phase I trials, with larger cohort studies with longer follow-up having only just commenced. More data from large trials on the safety and efficacy of FT are required before this approach can be recommended in men with PCa. Importantly, studies must confirm that no viable cancer cells remain in the region of ablation. FT might eventually prove to be a ‘middle ground’ between active surveillance and radical treatment, combining minimal morbidity with cancer control and the potential for retreatment.

Role of imaging and biopsy to assess local recurrence after definitive treatment for prostate carcinoma (surgery, radiotherapy, cryotherapy, HIFU)

PURPOSE

Defining the site of recurrent disease early after definitive treatment for a localized prostate cancer is a critical issue as it may greatly influence the subsequent therapeutic strategy or patient management.

METHODS

A systematic review of the literature was performed by searching Medline from January 1995 up to January 2011. Electronic searches were limited to the English language, and the keywords prostate cancer, radiotherapy [RT], high intensity focused ultrasound [HIFU], cryotherapy [CRIO], transrectal ultrasound [TRUS], magnetic resonance [MRI], PET/TC, and prostate biopsy were used.

RESULTS

Despite the fact that diagnosis of a local recurrence is based on PSA values and kinetics, imaging by means of different techniques may be a prerequisite for effective disease management. Unfortunately, prostate cancer local recurrences are very difficult to detect by TRUS and conventional imaging that have shown limited accuracy at least at early stages. On the contrary, functional and molecular imaging such as dynamic contrast-enhanced MRI (DCE-MRI), and diffusion-weighted imaging (DWI), offers the possibility of imaging molecular or cellular processes of individual tumors. Recently, PET/CT, using 11C-choline, 18F-fluorocholine or 11C-acetate has been successfully proposed in detecting local recurrences as well as distant metastases. Nevertheless, in controversial cases, it is necessary to perform a biopsy of the prostatic fossa or a biopsy of the prostate to assess the presence of a local recurrence under guidance of MRI or TRUS findings.

CONCLUSION

It is likely that imaging will be extensively used in the future to detect and localize prostate cancer local recurrences before salvage treatment.

Focal therapy in prostate cancer: modalities, findings and future considerations

Focal therapy is emerging as an alternative to active surveillance for the management of low-risk prostate cancer in carefully selected patients. The aim of focal therapy is long-term cancer control without the associated morbidity that plagues all radical therapies. Different energy modalities have been used to focally ablate cancer tissue, and available techniques include cryotherapy, laser ablation, high-intensity focused ultrasound and photodynamic therapy. The majority of evidence for focal therapy has come from case series and small phase I trials, and larger cohort studies with longer follow-up are only now being commenced. More data from large trials on the safety and efficacy of focal therapy are therefore required before this approach can be recommended in men with prostate cancer; in particular, studies must confirm that no viable cells remain in the region of ablation. Focal therapy might eventually prove to be a 'middle ground' between active surveillance and radical treatment, combining minimal morbidity with cancer control and the potential for re-treatment.

Candidate selection for prostate cancer focal therapy

Focal therapy has emerged as a potential treatment paradigm for men with localized prostate cancer, because it serves as a medium between the ambiguity of surveillance and the potential reduction of quality of life observed with radical treatment. Candidate selection remains the major challenge of implementing focal therapy in clinical practice. While focal therapy is potentially widely applicable, there is general consensus that initial efforts to initiate focal therapy protocols in practice should be limited to men with disease features that are low to low-intermediate risk, thereby limiting the likelihood of early systemic failure. Selection of candidates is first dependent on the intent of focal therapy. Curative intent focal therapy is limited to a small number of men with isolated, low-risk, unifocal, or unilateral disease. In men for whom local control-and potential prolongation of the natural history of disease-is desired, mapping strategies would focus on identification of the dominant site of disease and ruling out high-risk features. Tools such as conventional transrectal biopsy, transperineal saturation biopsy, and prostate MRI all have relative merits and shortcomings. While ultimately limitation of biopsy is desirable through combinations of transrectal biopsy and imaging, for now, limitations of conventional imaging modalities make it likely that most men will need transperineal saturation biopsy before inclusion in focal therapy protocols.

Focal laser ablation for prostate cancer followed by radical prostatectomy: validation of focal therapy and imaging accuracy

An increased incidence of low-risk prostate cancer (PCa) has led investigators to develop focal therapy as a management option for PCa. We evaluated the effects of focal laser ablation (FLA) on PCa tissue and the accuracy of magnetic resonance imaging (MRI) in determining ablated lesion volume by comparing the whole-mount histology and MRI in four patients that underwent FLA followed by radical prostatectomy. Ablated areas were characterized by homogeneous coagulation necrosis. The MRI-calculated ablated volume correlated well with histopathology. We found that FLA creates confluent ablation with no evidence of viable cells in treated regions. Postablation MRI is able to determine the ablation accurately.

Characterizing TUNA ablative treatments of the prostate for benign hyperplasia with gadolinium-enhanced magnetic resonance imaging

BACKGROUND AND PURPOSE

Transurethral Needle Ablation of the prostate TUNA has been accepted as an office-based treatment for benign prostatic hyperplasia (BPH) for many years. Clinical outcomes have been reported, but the amount and location of the necrosis produced have yet to be characterized. The necrosis caused by TUNA was evaluated by gadolinium-enhanced magnetic resonance imaging (MRI) of the pelvis.

PATIENTS AND METHODS

Twelve patients with BPH/lower urinary-tract symptoms underwent standard TUNA, and MRI scans with gadolinium enhancement were performed before and 1 week after treatment. The images were studied using Analyze software to quantify the amount of necrosis compared with the prostatic volume. Transverse, coronal, and sagittal images were obtained to identify the location of the necrosis.

RESULTS

New gadolinium defects were seen in all patients after TUNA. The lesions coalesced into continuous areas of necrosis and correlated with the site of needle placement. The mean volume of necrosis was 6.84 cc and equated to 8.6% of the prostate volume. No lesions were found near the apex, urethra, or rectum; and none extended beyond the prostate capsule.

CONCLUSIONS

Gadolinium-enhanced MRI demonstrates new vascular defects representing necrosis caused by TUNA of the prostate. This therapy for BPH produces necrotic lesions that can be placed strategically by the surgeon. The standard protocol produces lesions that coalesce to create larger lesions. This MRI study has characterized, for the first time, the heating pattern and intraprostatic necrosis of a complete TUNA procedure.

Diagnosis of prostatic carcinoma after therapy

CONTEXT

Prostate cancer is the most common cancer of men in the United States and is third only to lung and colon cancer as a cause of cancer death. In 2006, 27,350 Americans will die of prostate cancer, and 234,460 new cases will be diagnosed. Treatment changes in the benign and cancerous prostate create diagnostic challenges in pathologic interpretation, particularly in needle biopsy specimens and in evaluation of extraprostatic metastases.

OBJECTIVE

To summarize therapy-related pathologic findings in the prostate with emphasis on recognition of treated adenocarcinoma.

DATA SOURCES

Extensive review of published literature and the authors' experience.

CONCLUSIONS

Following therapy for prostate cancer, it is critical that the clinician provide the pertinent history of androgen deprivation or radiation therapy to assist the pathologist in rendering the correct diagnosis.

Interstitial temperature mapping during Prolieve transurethral microwave treatment: Imaging reveals thermotherapy temperatures resulting in tissue necrosis and patent prostatic urethra

OBJECTIVES

Temperature mapping of the prostate during transurethral microwave thermotherapy and imaging of the resultant zones of tissue necrosis have been previously performed using several commercial systems. This study was performed using the Prolieve Thermodilatation System, which simultaneously compresses the prostate with a 46F balloon circulating heated fluid and delivering microwave energy into the prostate.

METHODS

Interstitial temperature mapping during Prolieve treatment was performed on 10 patients with benign prostatic hyperplasia using 24 temperature sensors arrayed throughout the prostate. Voiding cystourethrograms were performed on 3 additional patients treated without temperature mapping to document the patency of the prostatic urethra 1 hour after treatment. Gadolinium-enhanced magnetic resonance imaging studies were performed on all patients 1 week after treatment to determine the extent and pattern of tissue necrosis resulting from transurethral microwave thermotherapy.

RESULTS

Interstitial temperature mapping found that the heating pattern generated by the Prolieve system created average peak temperatures of 51.8 degrees C an average of 7 mm away from the prostatic urethra. These temperatures were greater near the bladder neck and mid-gland than toward the prostatic apex. Subtherapeutic temperatures were seen adjacent to the urethra, consistent with the viable tissue seen on gadolinium-enhanced magnetic resonance imaging sequences. Magnetic resonance imaging also revealed necrotic zones that were consistent with sustained temperatures greater than 45 degrees C. Voiding cystourethrograms showed widely patent prostatic urethras 1 hour after treatment.

CONCLUSIONS

Transurethral microwave thermotherapy with the Prolieve Thermodilatation System produced sustained therapeutic temperatures that resulted in tissue necrosis while maintaining viable tissue surrounding a temporarily dilated prostatic urethra.

Magnetic resonance imaging correlated with the histopathological effect of Pd-bacteriopheophorbide (Tookad) photodynamic therapy on the normal canine prostate gland

BACKGROUND AND OBJECTIVE

To determine the optimal magnetic resonance imaging (MRI) methodology to assess photodynamic therapy (PDT)-induced histopathological responses in the prostate.

STUDY DESIGN/MATERIALS AND METHODS

Laparotomy was performed in five healthy dogs. Cylindrical diffuser was placed in the prostates to deliver light of 50-300 J/cm at 150 mW/cm and 763 nm to activate IV-injected Tookad (1 mg/kg b.w.). Fast spin echo (FSE) T2-weighted, post-contrast-enhanced T1-(CE-T1) and diffusion weighted images (DWI) were obtained pre- and 2 days, 7 days, and 1 month post-PDT. Radiological-histopathological correlation was performed at 7 days (n = 4) and 1 month (n = 1) after PDT. A qualitative assessment of signal changes and apparent diffusion coefficient (ADC) mapping was performed.

RESULTS

At 2 or 7 days post-PDT, there was good spatial correlation between PDT-induced hemorrhagic necrosis and unenhanced regions on CE-T1 images. There was a rapidly and persistently enhancing rim corresponding to edema and inflammation. FSE T2 and DWI showed altered signal but did not clearly define necrosis in all cases. At 1 month, it was hard to correlate MR images to histopathologic changes as they represented a mixture of necrosis and developing fibrosis, which led to a mixed signal intensity and less demarcated contrast enhancement.

CONCLUSIONS

At 7 days after PDT, gadolinium DTPA contrast-enhanced MRI is superior to DWI and T2 imaging in assessing the boundary of Tookad PDT-induced tissue necrosis in the normal canine prostate.

In vivo temperature mapping of prostate during treatment with TherMatrx TMx-2000 device: heat field and MRI determinations of necrotic lesions

BACKGROUND AND PURPOSE

The effectiveness of any thermotherapy device is determined by the temperatures created and how long they are applied. Understanding the heating characteristics of a thermotherapy device is vital to its correct implementation. Interstitial temperature mapping was used to determine the heat field created within the prostate by the TherMatrx TMx-2000 transurethral microwave thermotherapy (TUMT) device. Gadolinium-enhanced MRI was used to determine the extent, type, and pattern of coagulation necrosis caused by TUMT.

PATIENTS AND METHODS

Interstitial temperature mapping was performed during treatment in five patients with benign prostatic hyperplasia using 24 temperature sensors inserted through the perineum and arrayed throughout the prostate under ultrasound and X-ray guidance. Gadolinium-enhanced MRI scans were performed on all patients 1 week after treatment.

RESULTS

Interstitial temperature mapping found the heat field created to peak at the urethral surface near the central part of the catheter antenna. Temperatures decreased at consistent rates of 1 to 1.4 degrees C/mm radially and 0.1 to 0.5 degrees C/mm longitudinally from the peak area. Gadolinium-enhanced MRI showed minimal dispersed necrosis and only in the periurethral area.

CONCLUSIONS

The TMx-2000 can create temperatures >45 degrees C in areas 3 to 4 mm from the antenna. However, the heat pattern and protocol of the TMx-2000 produce necrosis-generating conditions only within a few millimeters of the urethra.

Cancer de la prostate : les aspects cliniques, biologiques et histopathologiques utiles au radiologue

Medical imaging has an important role in the diagnosis and treatment options of prostate cancer (TRUS guided biopsies, MRI). The knowledge of the different types of cancers, their preferred topography, imaging features, extension pattern, and also the important items that may help the surgical procedure (or any other treatment) are as many crucial key points for optimal management of patients.

Effects of spatial and temporal resolution for MR image-guided thermal ablation of prostate with transurethral ultrasound

PURPOSE

To describe approaches for determining optimal spatial and temporal resolutions for the proton resonance frequency shift method of quantitative magnetic resonance temperature imaging (MRTI) guidance of transurethral ultrasonic prostate ablation.

MATERIALS AND METHODS

Temperature distributions of two transurethral ultrasound applicators (90 degrees sectored tubular and planar arrays) for canine prostate ablation were measured via MRTI during in vivo sonication, and agree well with two-dimensional finite difference model simulations at various spatial resolutions. Measured temperature distributions establish the relevant signal-to-noise ratio (SNR) range for thermometry in an interventional MR scanner, and are reconstructed at different resolutions to compare resultant temperature measurements. Various temporal resolutions are calculated by averaging MRTI frames.

RESULTS

When noise is added to simulated temperature distributions for tubular and planar applicators, the minimum root mean squared (RMS) error is achieved by reconstructing to pixel sizes of 1.9 and 1.7 mm, respectively. In in vivo measurements, low spatial resolution MRTI data are shown to reduce the noise without significantly affecting thermal dose calculations. Temporal resolution of 0.66 frames/minute leads to measurement errors of more than 12 degrees C during rapid heating.

CONCLUSION

Optimizing MRTI pixel size entails balancing large pixel SNR gain with accuracy in representing underlying temperature distributions.

Relationship between tumour growth rate and carbogen-based functional MRI for a chemically induced HCC in mice

We previously performed MRI studies of HCC (hepatocellular carcinomas) in mice showing the feasibility of measuring a carbogen effect. In the present study carbogen response of the whole tumour was compared with growth characteristics during longitudinal follow-up. HCC were chemically induced. The imaging protocol at 4.7 T comprised a fast spin-echo sequence for high-resolution screening and measurement of growth curves, and a fast gradient echo sequence allowing an entire T2*w image acquisition per respiratory cycle to perform fMRI under carbogen breathing. A new parameter, T+, the fraction of tumour voxels with increased intensity under carbogen was measured on manually defined ROIs. Twenty-two HCC were followed for 3-10 weeks. Tumours were divided into two groups, "regularly" and "irregularly" growing tumours. A linear correlation between T+ and tumour growth rate was observed only for "regularly" growing HCC. These results suggest a link between tumour growth rates and tumour fractions exhibiting signal increase upon carbogen breathing. They are compatible with observations by others that rapidly growing tumours are more hypoxic than slowly growing ones. Combined measurement of T+ and tumour growth may become a useful noninvasive follow-up approach for assessment and/or management of therapies involving vasculature-targeting and anti-proliferative drugs.