By: Dan Sperling, MD

Multiparametric MRI (mpMRI) is rapidly becoming the imaging standard for the detection, localization and aggression information regarding prostate cancer (PCa). While not yet capable of the diagnostic characteristics afforded by a needle biopsy, an experienced radiological reader can interpret 3T mpMRI images with a very high degree of confidence. Readers are referred to https://sperlingprostatecenter.com/multiparametric-mri-useful-way-detect-significant-prostate-cancer/ for more information.

Another imaging technology that is gaining traction for detecting PCa in the pelvic region and lymph nodes is called Positron Emission Tomography (PET) scan. Unlike MRI, which involves no radioactivity, PET requires the intravenous injection of a pharmaceutical called a radiotracer. A radiotracer is a radioactive isotope bonded with molecules that are preferentially “taken up” by prostate cancer tumor cells. The radioactivity is then detected by the imaging device, and produced as color-coded images on a monitor. The tumor “lights up,” allowing detection. See earlier articles on PET for prostate cancer at https://sperlingprostatecenter.com/introduction-positron-emission-tomography-imaging-pet-scans/ and https://sperlingprostatecenter.com/choline-c-11-pet-scans-prostate-cancer/ .

When a patient presents with what appears to be high-risk PCa, a 3T mpMRI scan of the prostate and surrounding structures is essential to assist with treatment planning. Evidence of extracapsular extension may be a deciding factor in whether the patient is a candidate for radical prostatectomy. In addition, undergoing a PET scan using the isotope [18F]-fluorocholine or (18)F-FCholine can help to determine if cancer has spread to the local and regional lymph nodes. Based on clinical consensus, experts agree that in such cases it is not desirable to put a patient through surgical gland removal (prostatectomy) because the cancer has already metastasized.

A newly published French study[i] compares the diagnostic performance of diffusion-weighted MRI (DWI-MRI, a functional parameter that reveals the motion of water molecules in tissue to distinguish between healthy and malignant cells) vs. [18F]-fluorocholine PET-CT. Specifically, they were exploring how these two imaging modalities succeed in staging cancer by detecting tumor activity in local and regional lymph nodes before radical prostatectomy (RP) with extended pelvic lymph node removal (PLND) for pathology to analyze.

The researchers retrospectively identified 47 patients from May 2010 to December 2012 who had both (18)F-FCholine and DWI-MRI prior to surgery (either RP or PLND or both). To determine the success of the imaging, they correlated the findings from lab analysis of the surgical specimens (prostate gland, lymph nodes) with the two types of scanning in:

• Lymph node invasion
• Tumor presence in each of 6 prostate sections (sextants)
• Capsular invasion
• Tumor extension into the seminal vesicles

For comparison, they calculated the sensitivity (true positive) and specificity (true negative) rates of each.[ii]

The authors found that for tumor staging, DWI-MRI “showed better performances with a better specificity (69%) for sextants analysis and sensitivity to detect seminal vesicle invasion (73% vs. 36%).” However, (18)F-FCholine was more sensitive and specific for lymph node involvement, offering important additional information when staging high-risk PCa. The authors concluded that while giving valuable information, (18)F-FCholine “cannot replace MRI that remains better for tumoral localization and local evaluation, especially for seminal vesicle invasion.”

[i] Pinaquy JB, De Clermont-Galleran H, Pasticier G et al. Comparative effectiveness of [18 F]-fluorocholine PET-CT and pelvic MRI with diffusion-weighted imaging for staging in patients with high-risk prostate cancer. Prostate. 2015 Feb;75(3):323-31

[ii] From http://en.wikipedia.org/wiki/Sensitivity_and_specificity : Sensitivity … measures the proportion of actual positives which are correctly identified as such (e.g., the percentage of sick people who are correctly identified as having the condition)… Specificity …measures the proportion of negatives which are correctly identified as such (e.g., the percentage of healthy people who are correctly identified as not having the condition)…