Prostate focused ultrasound focal therapy—imaging for the future

Passive Elastography for Clinical HIFU Lesion Detection

High-intensity Focused Ultrasound (HIFU) is a promising treatment modality for a wide range of pathologies including prostate cancer. However, the lack of a reliable ultrasound-based monitoring technique limits its clinical use. Ultrasound currently provides real-time HIFU planning, but its use for monitoring is usually limited to detecting the backscatter increase resulting from chaotic bubble appearance. HIFU has been shown to generate stiffening in various tissues, so elastography is an interesting lead for ablation monitoring. However, the standard techniques usually require the generation of a controlled push which can be problematic in deeper organs. Passive elastography offers a potential alternative as it uses the physiological wave field to estimate the elasticity in tissues and not an external perturbation. This technique was adapted to process B-mode images acquired with a clinical system. It was first shown to faithfully assess elasticity in calibrated phantoms. The technique was then implemented on the Focal One® clinical system to evaluate its capacity to detect HIFU lesions in vitro (CNR = 9.2 dB) showing its independence regarding the bubbles resulting from HIFU and in vivo where the physiological wave field was successfully used to detect and delineate lesions of different sizes in porcine liver. Finally, the technique was performed for the very first time in four prostate cancer patients showing strong variation in elasticity before and after HIFU treatment (average variation of 33.0 ± 16.0 % ). Passive elastography has shown evidence of its potential to monitor HIFU treatment and thus help spread its use.

Simultaneous proton resonance frequency T1 - MR shear wave elastography for MR-guided focused ultrasound multiparametric treatment monitoring

PURPOSE

To develop an efficient MRI pulse sequence to simultaneously measure multiple parameters that have been shown to correlate with tissue nonviability following thermal therapies.

METHODS

A 3D segmented EPI pulse sequence was used to simultaneously measure proton resonance frequency shift (PRFS) MR thermometry (MRT), T1 relaxation time, and shear wave velocity induced by focused ultrasound (FUS) push pulses. Experiments were performed in tissue mimicking gelatin phantoms and ex vivo bovine liver. Using a carefully designed FUS triggering scheme, a heating duty cycle of approximately 65% was achieved by interleaving FUS ablation pulses with FUS push pulses to induce shear waves in the tissue.

RESULTS

In phantom studies, temperature increases measured with PRFS MRT and increases in T1 correlated with decreased shear wave velocity, consistent with material softening with increasing temperature. During ablation in ex vivo liver, temperature increase measured with PRFS MRT initially correlated with increasing T1 and decreasing shear wave velocity, and after tissue coagulation with decreasing T1 and increasing shear wave velocity. This is consistent with a previously described hysteresis in T1 versus PRFS curves and increased tissue stiffness with tissue coagulation.

CONCLUSION

An efficient approach for simultaneous and dynamic measurements of PRSF, T1 , and shear wave velocity during treatment is presented. This approach holds promise for providing co-registered dynamic measures of multiple parameters, which correlates to tissue nonviability during and following thermal therapies, such as FUS.

Learning Multiparametric Biomarkers for Assessing MR-Guided Focused Ultrasound Treatment of Malignant Tumors

Noninvasive MR-guided focused ultrasound (MRgFUS) treatments are promising alternatives to the surgical removal of malignant tumors. A significant challenge is assessing the viability of treated tissue during and immediately after MRgFUS procedures. Current clinical assessment uses the nonperfused volume (NPV) biomarker immediately after treatment from contrast-enhanced MRI. The NPV has variable accuracy, and the use of contrast agent prevents continuing MRgFUS treatment if tumor coverage is inadequate. This work presents a novel, noncontrast, learned multiparametric MR biomarker that can be used during treatment for intratreatment assessment, validated in a VX2 rabbit tumor model. A deep convolutional neural network was trained on noncontrast multiparametric MR images using the NPV biomarker from follow-up MR imaging (3-5 days after MRgFUS treatment) as the accurate label of nonviable tissue. A novel volume-conserving registration algorithm yielded a voxel-wise correlation between treatment and follow-up NPV, providing a rigorous validation of the biomarker. The learned noncontrast multiparametric MR biomarker predicted the follow-up NPV with an average DICE coefficient of 0.71, substantially outperforming the current clinical standard (DICE coefficient = 0.53). Noncontrast multiparametric MR imaging integrated with a deep convolutional neural network provides a more accurate prediction of MRgFUS treatment outcome than current contrast-based techniques.

Viscoelastic characterization of HIFU ablation with shear wave by using K-space analysis combined with model-fitting correction method

The viscoelastic properties of tissues can reflect human physiological and pathological conditions. During and after the high-intensity focused ultrasound (HIFU) treatment, measuring the viscoelasticity of HIFU ablated tissue is important for therapy evaluation. Two-dimensional Fourier transform (2DFT) method has been reported to quantify elasticity and viscosity. However, a deviation is induced by under-sampling in practical application. This work proposes an approach based on the convolution theorem and model fitting to solve the finite spatial data problem. A model using the convolution theorem was constructed, and mean-square error (MSE) was calculated to determine the optimal fitting between the model and experimental data. For validation, HIFU therapeutic experiments were conducted in polyacrylamide-bovine serum (BAS) transparent tissue-mimicking phantoms. This approach was used to quantify the viscoelasticity of HIFU ablation and untreated phantoms. Acoustic-radiation-force (ARF) shear wave was generated by the same HIFU therapeutic transducer, and laser Doppler vibrometer (LDV) was used for the high-resolution measurement of shear wave signals. Results suggest that the shear elasticity and viscosity of untreated phantoms are generally smaller than those of HIFU ablation. Thus, the proposed method may be helpful for HIFU treatment monitoring.

Magnetic Resonance Imaging Assessment After Therapy in Prostate Cancer

Prostate cancer is the fifth leading cause of death worldwide. A variety of treatment options is available for localized prostate cancer and may range from active surveillance to focal therapy or whole gland treatment, that is, surgery or radiotherapy. Serum prostate-specific antigen levels are an important tool to monitor treatment success after whole gland treatment, unfortunately prostate-specific antigen is unreliable after focal therapy. Multiparametric magnetic resonance imaging of the prostate is rapidly gaining field in the management of prostate cancer and may play a crucial role in the evaluation of recurrent prostate cancer. This article will focus on postprocedural magnetic resonance imaging after different forms of local therapy in patients with prostate cancer.

Comparative Study of Pulsed Versus Continuous High-Intensity Focused Ultrasound Ablation Using In Vitro and In Vivo Models

OBJECTIVES

To compare the efficacy of pulsed high-intensity focused ultrasound (PHIFU) versus continuous high-intensity focused ultrasound (CHIFU) ablation at identical doses.

METHODS

Continuous and pulsed HIFU (1200 J) at duty cycles (DCs) of 60% and 20% were examined for their capacity to ablate bovine liver tissue in vitro and rabbit liver tissue in vivo. After ablation, grayscale changes and pathologic characteristics were observed or measured, and the tissue necrosis volume, energy efficiency factor, and average grayscale density were calculated.

RESULTS

The pulsed mode generated greater liquefaction necrosis. An inconspicuous grayscale change was observed for PHIFU at a DC of 20% in some samples, which appeared as an elliptical cavity. The energy efficiency factor of PHIFU at a DC of 60% was significantly lower than that of CHIFU, as observed both in vitro and in vivo (P < .05). The grayscale value and average grayscale density in response to CHIFU were significantly greater than those in response to PHIFU (60% or 20%; P < .05). Histopathologic analysis revealed liquefaction necrosis in all PHIFU groups.

CONCLUSIONS

At identical doses, compared with CHIFU, a single session of PHIFU can generate liquefaction necrosis and at a higher DC can improve ablation efficiency. This increased efficacy of PHIFU may involve enhancement of tissue destruction by cavitation effects and a reduction in the obstruction effect of endogenous microbubbles through cavitation effects or a more effective diffusion of heat.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.

A variable flip angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonant frequency shift and T1 -based thermometry

PURPOSE

To develop and evaluate a variable-flip-angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonance frequency shift (PRF) and T₁ -based thermometry in aqueous and adipose tissues, respectively.

METHODS

The proposed technique acquires multiecho radial k-space data in segments with alternating flip angles to measure 3D temperature maps dynamically on the basis of PRF and T₁ . A sliding-window k-space weighted image contrast filter is used to increase temporal resolution. PRF is measured in aqueous tissues and T₁ in adipose tissues using fat/water masks. The accuracy for T₁ quantification was evaluated in a reference T₁ /T₂ phantom. In vivo nonheating experiments were conducted in healthy subjects to evaluate the stability of PRF and T₁ in the brain, prostate, and breast. The proposed technique was used to monitor high-intensity focused ultrasound (HIFU) ablation in ex vivo porcine fat/muscle tissues and compared to temperature probe readings.

RESULTS

The proposed technique achieved 3D coverage with 1.1-mm to 1.3-mm in-plane resolution and 2-s to 5-s temporal resolution. During 20 to 30 min of nonheating in vivo scans, the temporal coefficient of variation for T₁ was <5% in the brain, prostate, and breast fatty tissues, while the standard deviation of relative PRF temperature change was within 3°C in aqueous tissues. During ex vivo HIFU ablation, the temperatures measured by PRF and T₁ were consistent with temperature probe readings, with an absolute mean difference within 2°C.

CONCLUSION

The proposed technique achieves simultaneous PRF and T₁ -based dynamic 3D MR temperature mapping in aqueous and adipose tissues. It may be used to improve MRI-guided thermal procedures.

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.

Multimodal Imaging in Focal Therapy Planning and Assessment in Primary Prostate Cancer

PURPOSE

There is increasing interest in focal therapy (male lumpectomy) of localized low-intermediate risk prostate cancer. Focal therapy is typically associated with low morbidity and provides the possibility of retreatment. Imaging is pivotal in stratification of men with localized prostate cancer for active surveillance, focal therapy or radical intervention. This article provides a concise review of focal therapy and the evolving role of imaging in this clinical setting.

METHODS

We performed a narrative and critical literature review by searching PubMed/Medline database from January 1997 to January 2017 for articles in the English language and the use of search keywords "focal therapy", "prostate cancer", and "imaging".

RESULTS

Most imaging studies are based on multiparametric magnetic resonance imaging. Transrectal ultrasound is inadequate independently but multiparametric ultrasound may provide new prospects. Positron emission tomography with radiotracers targeted to various underlying tumor biological features may provide unprecedented new opportunities. Multimodal Imaging appears most useful in localization of intraprostatic dominant index lesions amenable to focal therapy, in early assessment of therapeutic efficacy and potential need for additional focal treatments or transition to whole-gland therapy, and in predicting short-term and long-term outcomes.

CONCLUSION

Multimodal imaging is anticipated to play an increasing role in the focal therapy planning and assessment of low-intermediate risk prostate cancer and thereby moving this form of treatment option forward in the clinic.

Accuracy of Elastic Fusion of Prostate Magnetic Resonance and Transrectal Ultrasound Images under Routine Conditions: A Prospective Multi-Operator Study

Purpose

To evaluate in unselected patients imaged under routine conditions the co-registration accuracy of elastic fusion between magnetic resonance (MR) and ultrasound (US) images obtained by the Koelis Urostation^™.

Materials and Methods

We prospectively included 15 consecutive patients referred for placement of intraprostatic fiducials before radiotherapy and who gave written informed consent by signing the Institutional Review Board-approved forms. Three fiducials were placed in the prostate under US guidance in standardized positions (right apex, left mid-gland, right base) using the Koelis Urostation^™. Patients then underwent prostate MR imaging. Four operators outlined the prostate on MR and US images and an elastic fusion was retrospectively performed. Fiducials were used to measure the overall target registration error (TRE_3D), the error along the antero-posterior (TRE_AP), right-left (TRE_RL) and head-feet (TRE_HF) directions, and within the plane orthogonal to the virtual biopsy track (TRE_2D).

Results

Median TRE_3D and TRE_2D were 3.8–5.6 mm, and 2.5–3.6 mm, respectively. TRE_3D was significantly influenced by the operator (p = 0.013), fiducial location (p = 0.001) and 3D axis orientation (p<0.0001). The worst results were obtained by the least experienced operator. TRE_3D was smaller in mid-gland and base than in apex (average difference: -1.21 mm (95% confidence interval (95%CI): -2.03; -0.4) and -1.56 mm (95%CI: -2.44; -0.69) respectively). TRE_AP and TRE_HF were larger than TRE_RL (average difference: +1.29 mm (95%CI: +0.87; +1.71) and +0.59 mm (95%CI: +0.1; +0.95) respectively).

Conclusions

Registration error values were reasonable for clinical practice. The co-registration accuracy was significantly influenced by the operator’s experience, and significantly poorer in the antero-posterior direction and at the apex.

Cluster analysis of DCE-MRI data identifies regional tracer-kinetic changes after tumor treatment with high intensity focused ultrasound

Evaluation of high intensity focused ultrasound (HIFU) treatment with MRI is generally based on assessment of the non-perfused volume from contrast-enhanced T1-weighted images. However, the vascular status of tissue surrounding the non-perfused volume has not been extensively investigated with MRI. In this study, cluster analysis of the transfer constant K(trans) and extravascular extracellular volume fraction ve , derived from dynamic contrast-enhanced MRI (DCE-MRI) data, was performed in tumor tissue surrounding the non-perfused volume to identify tumor subregions with distinct contrast agent uptake kinetics. DCE-MRI was performed in CT26.WT colon carcinoma-bearing BALB/c mice before (n = 12), directly after (n = 12) and 3 days after (n = 6) partial tumor treatment with HIFU. In addition, a non-treated control group (n = 6) was included. The non-perfused volume was identified based on the level of contrast enhancement. Quantitative comparison between non-perfused tumor fractions and non-viable tumor fractions derived from NADH-diaphorase histology showed a stronger agreement between these fractions 3 days after treatment (R(2) to line of identity = 0.91) compared with directly after treatment (R(2) = 0.74). Next, k-means clustering with four clusters was applied to K(trans) and ve parameter values of all significantly enhanced pixels. The fraction of pixels within two clusters, characterized by a low K(trans) and either a low or high ve , significantly increased after HIFU. Changes in composition of these clusters were considered to be HIFU induced. Qualitative H&E histology showed that HIFU-induced alterations in these clusters may be associated with hemorrhage and structural tissue disruption. Combined microvasculature and hypoxia staining suggested that these tissue changes may affect blood vessel functionality and thereby tumor oxygenation. In conclusion, it was demonstrated that, in addition to assessment of the non-perfused tumor volume, the presented methodology gives further insight into HIFU-induced effects on tumor vascular status. This method may aid in assessment of the consequences of vascular alterations for the fate of the tissue.

MRI methods for the evaluation of high intensity focused ultrasound tumor treatment: Current status and future needs

Thermal ablation with high intensity focused ultrasound (HIFU) is an emerging noninvasive technique for the treatment of solid tumors. HIFU treatment of malignant tumors requires accurate treatment planning, monitoring and evaluation, which can be facilitated by performing the procedure in an MR-guided HIFU system. The MR-based evaluation of HIFU treatment is most often restricted to contrast-enhanced T1 -weighted imaging, while it has been shown that the non-perfused volume may not reflect the extent of nonviable tumor tissue after HIFU treatment. There are multiple studies in which more advanced MRI methods were assessed for their suitability for the evaluation of HIFU treatment. While several of these methods seem promising regarding their sensitivity to HIFU-induced tissue changes, there is still ample room for improvement of MRI protocols for HIFU treatment evaluation. In this review article, we describe the major acute and delayed effects of HIFU treatment. For each effect, the MRI methods that have been-or could be-used to detect the associated tissue changes are described. In addition, the potential value of multiparametric MRI for the evaluation of HIFU treatment is discussed. The review ends with a discussion on future directions for the MRI-based evaluation of HIFU treatment.

How accurate is multiparametric MR imaging in evaluation of prostate cancer volume?

PURPOSE

To assess the factors influencing multiparametric (MP) magnetic resonance (MR) imaging accuracy in estimating prostate cancer histologic volume (Vh).

MATERIALS AND METHODS

A prospective database of 202 patients who underwent MP MR imaging before radical prostatectomy was retrospectively used. Institutional review board approval and informed consent were obtained. Two independent radiologists delineated areas suspicious for cancer on images (T2-weighted, diffusion-weighted, dynamic contrast material-enhanced [DCE] pulse sequences) and scored their degree of suspicion of malignancy by using a five-level Likert score. One pathologist delineated cancers on whole-mount prostatectomy sections and calculated their volume by using digitized planimetry. Volumes of MR true-positive lesions were measured on T2-weighted images (VT2), on ADC maps (VADC), and on DCE images [VDCE]). VT2, VADC, VDCE and the greatest volume determined on images from any of the individual MR pulse sequences (Vmax) were compared with Vh (Bland-Altman analysis). Factors influencing MP MR imaging accuracy, or A, calculated as A = Vmax/Vh, were evaluated using generalized linear mixed models.

RESULTS

For both readers, Vh was significantly underestimated with VT2 (P < .0001, both), VADC (P < .0001, both), and VDCE (P = .02 and P = .003, readers 1 and 2, respectively), but not with Vmax (P = .13 and P = .21, readers 1 and 2, respectively). Mean, 25th percentile, and 75th percentile, respectively, for Vmax accuracy were 0.92, 0.54, and 1.85 for reader 1 and 0.95, 0.57, and 1.77 for reader 2. At generalized linear mixed (multivariate) analysis, tumor Likert score (P < .0001), Gleason score (P = .009), and Vh (P < .0001) significantly influenced Vmax accuracy (both readers). This accuracy was good in tumors with a Gleason score of 7 or higher or a Likert score of 5, with a tendency toward underestimation of Vh; accuracy was poor in small (<0.5 cc) or low-grade (Gleason score ≤6) tumors, with a tendency toward overestimation of Vh.

CONCLUSION

Vh can be estimated by using Vmax in aggressive tumors or in tumors with high Likert scores.

Characterization of prostate lesions as benign or malignant at multiparametric MR imaging: comparison of three scoring systems in patients treated with radical prostatectomy

PURPOSE

To compare the subjective Likert score to the Prostate Imaging Reporting and Data System (PIRADS) and morphology-location-signal intensity (MLS) scores for categorization of prostate lesions as benign or malignant at multiparametric magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Two hundred fifteen patients who underwent T2-weighted, diffusion-weighted, and dynamic contrast material-enhanced multiparametric MR imaging of the prostate before radical prostatectomy were included in a prospective database after they signed the institutional review board-approved forms. Senior readers 1 and 2 prospectively noted the location, shape, and signal intensity of lesions on MR images from individual pulse sequences and scored each for likelihood of malignancy by using a Likert scale (range, 1-5). A junior reader (reader 3) retrospectively reviewed the database and did the same analysis. The MLS score (range, 1-13) was computed by using the readers' descriptions of the lesions. Then, the three readers again scored the lesions they described by using the PIRADS score (range, 3-15). MLS and PIRADS scores were compared with the Likert score by using their areas under the receiver operating characteristic curves.

RESULTS

Areas under the receiver operating characteristic curves of the Likert, MLS, and PIRADS scores were 0.81, 0.77 (P = .03), and 0.75 (P = .01) for reader 1; 0.88, 0.74 (P < .0001), and 0.76 (P < .0001) for reader 2; and 0.81, 0.78 (P = .23), and 0.75 (P = .01) for reader 3. For diagnosing cancers with Gleason scores greater than or equal to 7, the Likert score was significantly more accurate than the others, except for the MLS score for reader 3. Weighted κ values were 0.470-0.524, 0.405-0.430, and 0.378-0.441 for the Likert, MLS, and PIRADS scores, respectively.

CONCLUSION

The Likert score allowed significantly more accurate categorization of prostate lesions on MR images than did the MLS and PIRADS scores.

Multiparametric MRI analysis for the identification of high intensity focused ultrasound-treated tumor tissue

Purpose

In this study endogenous magnetic resonance imaging (MRI) biomarkers for accurate segmentation of High Intensity Focused Ultrasound (HIFU)-treated tumor tissue and residual or recurring non-treated tumor tissue were identified.

Methods

Multiparametric MRI, consisting of quantitative T₁, T₂, Apparent Diffusion Coefficient (ADC) and Magnetization Transfer Ratio (MTR) mapping, was performed in tumor-bearing mice before (n = 14), 1 h after (n = 14) and 72 h (n = 7) after HIFU treatment. A non-treated control group was included (n = 7). Cluster analysis using the Iterative Self Organizing Data Analysis (ISODATA) technique was performed on subsets of MRI parameters (feature vectors). The clusters resulting from the ISODATA segmentation were divided into a viable and non-viable class based on the fraction of pixels assigned to the clusters at the different experimental time points. ISODATA-derived non-viable tumor fractions were quantitatively compared to histology-derived non-viable tumor volume fractions.

Results

The highest agreement between the ISODATA-derived and histology-derived non-viable tumor fractions was observed for feature vector {T₁, T₂, ADC}. R₁ (1/T₁), R₂ (1/T₂), ADC and MTR each were significantly increased in the ISODATA-defined non-viable tumor tissue at 1 h after HIFU treatment compared to viable, non-treated tumor tissue. R₁, ADC and MTR were also significantly increased at 72 h after HIFU.

Conclusions

This study demonstrates that non-viable, HIFU-treated tumor tissue can be distinguished from viable, non-treated tumor tissue using multiparametric MRI analysis. Clinical application of the presented methodology may allow for automated, accurate and objective evaluation of HIFU treatment.

Prostate focal peripheral zone lesions: characterization at multiparametric MR imaging--influence of a computer-aided diagnosis system

PURPOSE

To assess the impact of a computer-aided diagnosis (CAD) system in the characterization of focal prostate lesions at multiparametric magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Formal institutional review board approval was not required. Thirty consecutive 1.5-T multiparametric MR imaging studies (with T2-weighted, diffusion-weighted, and dynamic contrast material-enhanced imaging) obtained before radical prostatectomy in patients between September 2008 and February 2010 were reviewed. Twelve readers assessed the likelihood of malignancy of 88 predefined peripheral zone lesions by using a five-level (level, 0-4) subjective score (SS) in reading session 1. This was repeated 5 weeks later in reading session 2. The CAD results were then disclosed, and in reading session 3, the readers could amend the scores assigned during reading session 2. Diagnostic accuracy was assessed by using a receiver operating characteristic (ROC) regression model and was quantified with the area under the ROC curve (AUC).

RESULTS

Mean AUCs were significantly lower for less experienced (<1 year) readers (P < .02 for all sessions). Seven readers improved their performance between reading sessions 1 and 2, and 12 readers improved their performance between sessions 2 and 3. The mean AUCs for reading session 1 (83.0%; 95% confidence interval [CI]: 77.9%, 88.0%) and reading session 2 (84.1%; 95% CI: 78.1%, 88.7%) were not significantly different (P = .76). Although the mean AUC for reading session 3 (87.2%; 95% CI: 81.0%, 92.0%) was higher than that for session 2, the difference was not significant (P = .08). For an SS positivity threshold of 3, the specificity of reading session 2 (79.0%; 95% CI: 71.1%, 86.4%) was not significantly different from that of session 1 (78.7%; 95% CI: 70.5%, 86.8%) but was significantly lower than that of session 3 (86.2%; 95% CI: 77.1%, 93.1%; P < .03). The sensitivity of reading session 2 (68.4%; 95% CI: 57.5%, 77.7%) was significantly higher than that of session 1 (64.0%; 95% CI: 52.9%, 73.9%; P = .003) but was not significantly different from that of session 3 (71.4%; 95% CI: 58.3%, 82.7%).

CONCLUSION

A CAD system may improve the characterization of prostate lesions at multiparametric MR imaging by increasing reading specificity.

Focal therapy in prostate cancer: international multidisciplinary consensus on trial design

BACKGROUND

Focal therapy has been introduced for the treatment of localised prostate cancer (PCa). To provide the necessary data for consistent assessment, all focal therapy trials should be performed according to uniform, systematic pre- and post-treatment evaluation with well-defined end points and strict inclusion and exclusion criteria.

OBJECTIVE

To obtain consensus on trial design for focal therapy in PCa.

DESIGN, SETTING, AND PARTICIPANTS

A four-staged consensus project based on a modified Delphi process was conducted in which 48 experts in focal therapy of PCa participated. According to this formal consensus-building method, participants were asked to fill out an iterative sequence of questionnaires to collect data on trial design. Subsequently, a consensus meeting was held in which 13 panellists discussed acquired data, clarified the results, and defined the conclusions.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

A multidisciplinary board from oncologic centres worldwide reached consensus on patient selection, pretreatment assessment, evaluation of outcome, and follow-up.

RESULTS AND LIMITATIONS

Inclusion criteria for candidates in focal therapy trials are patients with prostate-specific antigen <15 ng/ml, clinical stage T1c-T2a, Gleason score 3+3 or 3+4, life expectancy of >10 yr, and any prostate volume. The optimal biopsy strategy includes transrectal ultrasound-guided biopsies to be taken between 6 mo and 12 mo after treatment. The primary objective should be focal ablation of clinically significant disease with negative biopsies at 12 mo after treatment as the primary end point.

CONCLUSIONS

This consensus report provides a standard for designing a feasible focal therapy trial.

PATIENT SUMMARY

A variety of ablative technologies have been introduced and applied in a focal manner for the treatment of prostate cancer (PCa). In this consensus report, an international panel of experts in the field of PCa determined pre- and post-treatment work-up for focal therapy research.