Accurate tumor staging for unfavorable intermediate- and high-risk prostate cancer
patients should underpin both prognostication and management decisions. This void
necessitates evaluation of the local, primary disease as well as spread to distant sites
including lymph nodes and possible distant metastases.
Multi-parametric magnetic resonance imaging (mp-MRI) has become the reference standard
practice for local imaging-based assessment in prostate cancer (PCa). Whole-body MRI
(WB-MRI) is seeing growing for detection of distant, metastatic disease, and is
particularly suited to detection of bone metastases, which are common in PCa. The
possibility of a one-stop staging modality has been raised, wherein mp-MRI + whole body
MRI (WB-MRI) would be used to further assess nodal and metastatic disease status in a
single sitting. Currently however, international guidelines consider bone scintigraphy
(BS) and pelvic computed tomography (CT) for distant disease to be the mainstays of
imaging-based staging decisions. A further concern with transitioning to All-in-One
prostate staging with MRI relates to the duration of scanning required, as an excessive
scan duration is likely to lead to patient discomfort, motion and consequently reduce
image quality.
The prostate imaging reporting and data system (PI-RADS) v2.1 standard published by
Turkbey et al. provides guidelines for mp-MRI of the prostate that are widely used as the
basis for assessment of local, primary PCa. Recent evidence suggests that some components
of the PI-RADS mp-MRI protocol are of little or no benefit to men with a very high risk
of aggressive PCa, defined as prostate specific antigen (PSA) ≥10 ng/mL and + digital
rectal exam, even before initial biopsy or repeated biopsy. In particular, dynamic
contrast enhanced (DCE) imaging and T2-weighted images (T2WI) in a third orthogonal plane
does not improve the overall accuracy of mp-MRI. Therefore, biparametric MRI (bp-MRI;
i.e. T2WI in two planes, diffusion-weighted imaging (DWI, without contrast agent
injection)) has been suggested to reduce examination time and cost, while retaining
sufficient diagnostic accuracy to "rule out" high-grade PCa in biopsy-naïve men.
WB-MRI offers greater sensitivity and diagnostic accuracy for bone and nodal disease than
BS and conventional CT. Further, a meta-analysis by Woo et al. has shown MRI (DWI +
conventional sequences) to have excellent sensitivity and specificity in particular for
detection of bone metastases in patients with PCa. The pooled per-patient sensitivity and
specificity of MRI in the 10 studies included in the meta-analysis were 0.96 (95%
confidence interval (CI) 0.87-0.99) and 0.98 (95% CI 0.93-0.99), respectively. Similar
performance for WB-MRI is reported in the meta-analysis of Shen et al. who found the
diagnostic performance of WB-MRI to be similar to that of choline PET/CT, with both being
superior to BS in the detection of bone metastases. The pooled sensitivities and
specificities in this meta-analysis were 0.97/0.95 and 0.79/0.82 for WB-MRI and BS
respectively. WB-MRI appears to be more accurate than conventional CT, which not
surprising the pooled sensitivities and specificities of CT alone have been reported as
0.42 and 0.82 in a pair of meta-analyses . A recent work by Johnston et al., found that a
WB-MRI protocol consisting of unenhanced T1-weighted DIXON and diffusion-weighted scans
provides much higher diagnostic accuracy than BS (sensitivity/specificity 0.90/0.88 vs
0.60/1.00) for the primary staging of intermediate- and high-risk PCa. They also found
high and very similar sensitivities/specificities for WB-MRI and BS in respect to nodal
disease, with values of 1.00/0.96 and 1.00/0.82 for N1 disease and 0.75/ 0.93 and
0.75/0.92 for M1a disease respectively.
The investigators are continuing their studies into the role and the added value of
WB-MRI in oncologic patients with advanced cancer (prostate, breast, melanoma],
lymphoma).
The investigators propose to evaluate the sensitivity of a protocol that combines bp-MRI
of the prostate, following the PI-RADS v2.1 guideline, with WB-MRI based on MET-RADS-P
guidelines, for an All-in-One, local and systemic staging of unfavorable intermediate-
and high-risk prostate cancer patients and to compare the results of systemic staging
with those obtained with CT and BS in the standard staging pathway. The combination of
bp-MRI and WB-MRI is expected to require a scan time of roughly 40 minutes, allowing it
to be performed in a conventional mp-MRI scan time allotment.
