Juan C. Camacho1,2, Nima Kokabi1, Peter A. Harri1, Tracy E. Powell2, and Sherif G. Nour1,2
1Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, United States, 2Interventional MRI Program, Emory University Hospital, Atlanta, GA, United States
Synopsis
The study objective is to investigate
magnetic resonance Apparent Diffusion Coefficient Quantification (ADC) in prostate
lesions and to correlate the values with the results of MRI-guided prostate targeted
sampling. A prospective cohort of patients presenting
with persistently elevated or rising serum prostate specific antigen (PSA) and
at least one lesion suspicious for prostate cancer that underwent MRI guided
targeted biopsy was evaluated. Thirty-five consecutive
patients were recruited presenting with 179 suspicious lesions. ROC curve analysis demonstrates that ADC predicts the
presence of malignancy and allows grade stratification and therefore, behaves
as a non-invasive imaging biomarker.Background and purpose
Prostate
cancer is the most common solid organ cancer in men (1). The main objective of
current non-invasive imaging techniques is to detect early-stage disease that
is biologically aggressive in an attempt to offer timely curative treatments. The currently used screening
and diagnostic tools include digital rectal examination; serum
prostate-specific antigen (PSA) and non-targeted transrectal ultrasound
(TRUS)–guided biopsy (3). Because of the limitations and poor specificity of
the available diagnostic tools, significant efforts are being made into
improving prostate cancer detection. It has been postulated that multiparametric
MRI is useful in the detection and risk stratification of prostate cancer (4) and
also, that MRI can serve as a real-time guide to adequately sample suspicious
lesions in the prostate (5). Therefore, the objective of this study is to investigate magnetic resonance diffusion weighted
imaging (DWI) quantification (or Apparent Diffusion Coefficient Quantification
(ADC)) in suspicious prostate lesions as an imaging biomarker of malignancy,
and to correlate the values with the results of MRI-guided prostate targeted
sampling.
Materials and Methods
IRB approved HIPAA
compliant retrospective review of a 12-month period prospective cohort of
patients presenting
with persistently elevated or rising serum prostate specific antigen (PSA) and
at least one lesion suspicious for prostate cancer that underwent MRI guided
targeted biopsy. Diagnostic and interventional procedures were performed using a 32-element surface
pelvic array coil on a 3T MAGNETOM Trio system (Siemens Medical Solutions,
Erlangen, Germany). Single
shot echo planar DWI was performed with tridimensional diffusion-encoding
gradients utilizing b-values of 0, 1000, 1500 and 2000 s/mm
2 (TR = 6000
ms / TE = 89 ms / NSA = 7 / FOV = 300 mm / phase over sampling = 50% / slice
thickness = 3 mm / BW = 1736 / base resolution = 160 / Ipat = 2 / TA = 7:20 min).
Subsequent targeted
biopsies of suspicious lesions were performed following transrectal placement of
a Dyna-TRIM biopsy system (Invivo, Gainesville, FL). Pre-procedural imaging allowed
identification of the transrectal fiducial line, target lesions, and
tridimensional trajectory. Pathology results per lesion were correlated to
pre-procedural ADC quantification. ADC was measured by placing a region of interest
(ROI) in each lesion and in normal prostate tissue within the central and
peripheral zones to assure consistency in each patient. Correlation between ADC values of tumors and
anatomic pathology was evaluated with paired t-test. Receiver operating characteristic (ROC) curves
were made to analyze ADC performance in discriminating low- and high-grade
tumors (α=0.05).
Results
Thirty-five
consecutive patients were recruited (mean age 63, range 55-82). Average PSA
level was 9.3 ng/mL (median 7.76 ng/mL; SD 6.4 ng/mL). 179 suspicious lesions were successfully
biopsied (Average number of lesions per patient 5, range 2-8) and all samples
were deemed diagnostic. ADC values of the normal tissue in the central zone were
significantly lower when compared to the peripheral gland (ADC value of the peripheral
zone was 1,27 mm
2/sec vs. ADC value of the central gland 0,97 mm
2/sec,
p<0.001). Overall cancer detection rate was 19/35
(54.2%). Pathology results were benign (inflammation) in 133 lesions (74.3%),
and malignant in 43 lesions (24.7%), with low-grade cancer (Gleason score 6) in
12/179 (6.7%); and intermediate to high-grade cancer (Gleason score > 7) in
31/179 (17.3%). ADC values of intermediate and high-grade lesions (mean ADC
= 0.685 mm
2/sec,
SD 0.109 mm
2/sec) were significantly lower than low-grade lesions (mean ADC = 0.767 mm
2/sec, SD 0.080
mm
2/sec; p = 0.01). Also, all grades of prostate
cancers demonstrated significantly restricted diffusion compared to benign
lesions (mean ADC=0.877 mm
2/sec, SD 0.162 mm
2/sec; p <0.001). ROC curves
are shown below (Figures 1 and 2). Figure 3 illustrates an example of a malignant lesion.
Conclusion
Non-invasive
quantitative ADC measurement is a reliable imaging biomarker for predicting
malignancy and stratifying cancer risk in patients with persistently elevated
or rising serum prostate specific antigen (PSA) levels and suspicious focal
prostate abnormalities undergoing targeted tissue sampling under MRI guidance.
Acknowledgements
No financial support was received for this clinical study. The location of the study, the
facilities and the study subjects were recruited at Emory University Affiliated
Hospitals, Atlanta, Georgia, US.References
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