Faculty Bibliography

AIM: To evaluate the performance of normalised apparent diffusion coefficient (ADC) values for prostate cancer assessment when performed by independent observers blinded to histopathology findings. MATERIALS AND METHODS: Fifty-eight patients undergoing 3 T phased-array coil magnetic resonance imaging (MRI) including diffusion-weighted imaging (DWI; maximal b-value 1000 s/mm2) before prostatectomy were included. Two radiologists independently evaluated the images, unaware of the histopathology findings. Regions of interest (ROIs) were drawn within areas showing visually low ADC within the peripheral zone (PZ) and transition zone (TZ) bilaterally. ROIs were also placed within regions in both lobes not suspicious for tumour, allowing computation of normalised ADC (nADC) ratios between suspicious and non-suspicious regions. The diagnostic performance of ADC and nADC were compared. RESULTS: For PZ tumour detection, ADC achieved significantly higher area under the receiver operating characteristic curve (AUC; p=0.026) and specificity (p=0.021) than nADC for reader 1, and significantly higher AUC (p=0.025) than nADC for reader 2. For TZ tumour detection, nADC achieved significantly higher specificity (p=0.003) and accuracy (p=0.004) than ADC for reader 2. For PZ Gleason score >3+3 tumour detection, ADC achieved significantly higher AUC (p=0.003) and specificity (p=0.005) than nADC for reader 1, and significantly higher AUC (p=0.023) than nADC for reader 2. For TZ Gleason score >3+3 tumour detection, ADC achieved significantly higher specificity (p=0.019) than nADC for reader 1. CONCLUSION: In contrast to prior studies performing unblinded evaluations, ADC was observed to outperform nADC overall for two independent observers blinded to the histopathology findings. Therefore, although strategies to improve the utility of ADC measurements in prostate cancer assessment merit continued investigation, caution is warranted when applying normalisation to improve diagnostic performance in clinical practice.

PURPOSE: To compare boundaries of prostate tumors on MRI and histologic assessment from radical prostatectomy (RP) using detailed software-assisted co-registration, in order to define an optimal treatment margin to achieve complete tumor destruction during image-guided focal ablation. METHODS: 33 patients who underwent 3T MRI before RP were included. A radiologist traced lesion borders on MRI and assigned a suspicion score (SS) from 2-5. 3D reconstructions were created from high-resolution digitalized slides from RP specimens and co-registered to MRI using advanced software. Tumors were compared between histology and MRI using the Hausdorff Distance (HD) and stratified by MRI-SS, Gleason Score (GS), and lesion diameter. Cylindrical volume estimates of treatment effects were used to define the optimal treatment margin. RESULTS: 46 histologically confirmed cancers underwent 3D software-based registration with MRI. MRI underestimated tumor sizes, with the maximal discrepancy between MRI and histologic boundaries for a given tumor averaging 1.99+/-3.1mm (18.5% of the MRI diameter). Boundary underestimation was larger for MRI-SS>/=4 lesions (+3.49+/-2.1mm; p<0.001) and GS>/=7 lesions (+2.48+/-2.8mm; p 0.035). On average, a simulated cylindrical treatment volume based on the MRI boundary missed 14.8% of the tumor volume compared with a simulated cylindrical volume based on the histologic boundary. A simulated treatment volume based on a 9mm treatment margin achieved complete histologic tumor destruction in 100% of patients. CONCLUSION: MRI underestimates histologically-determined tumor boundaries, especially for high MRI-SS and high GS lesions. A 9mm treatment margin around an MRI-visible lesion consistently ensures treatment of the entire histologic tumor volume during focal ablative therapy.

The contemporary management of prostate cancer (PCa) has been criticized as fostering overdetection and overtreatment of indolent disease. In particular, the historical inability to identify those men with an elevated PSA who truly warrant biopsy, and, for those needing biopsy, to localize aggressive tumors within the prostate, has contributed to suboptimal diagnosis and treatment strategies. This article describes how modern multi-parametric MRI of the prostate addresses such challenges and reduces both overdiagnosis and overtreatment. The central role of diffusion-weighted imaging (DWI) in contributing to MRI's current impact is described. Prostate MRI incorporating DWI achieves higher sensitivity than standard systematic biopsy for intermediate-to-high risk tumor, while having lower sensitivity for low-grade tumors that are unlikely to impact longevity. Particular applications of prostate MRI that are explored include selection of a subset of men with clinical suspicion of PCa to undergo biopsy as well as reliable confirmation of only low-risk disease in active surveillance patients. Various challenges to redefining the standard of care to incorporate solely MRI-targeted cores, without concomitant standard systematic cores, are identified. These include needs for further technical optimization of current systems for performing MRI-targeted biopsies, enhanced education and expertise in prostate MRI among radiologists, greater standardization in prostate MRI reporting across centers, and recognition of the roles of pre-biopsy MRI and MRI-targeted biopsy by payers. Ultimately, it is hoped that the medical community in the United States will embrace prostate MRI and MRI-targeted biopsy, allowing all patients with known or suspected prostate cancer to benefit from this approach.