Introduction

Multiparametric MRI (mpMRI) has become the preferred method for detecting prostate cancer (PCa) foci after a negative biopsy and has been incorporated into EAU guidelines. Although the NPV of mpMRI is around 90-95%, some, potentially important, cancers may be mpMRI-invisible. Some men may have contraindications to MRI (i.e. claustrophobic patients or presence of metallic implants). 11C-choline PET is a promising tool for the investigation of PCa but studies have provided equivocal results because of overlap with benign prostate hyperplasia (BPH) and prostatitis. The aim of this study was to assess the potential clinical impact of 11C-choline PET/TRUS fusion-guided prostate biopsy in men with persistently elevated PSA after negative biopsy and negative or contra-indicated mpMRI.

Methods

Clinical data were acquired as part of a prospective ongoing observational study: MpMRI_ICH_1398; Ethical Committee approval March 2015. Patients with persistently elevated PSA, with or without ASAP and/or HG-PIN and negative DRE, after at least one negative biopsy (at least 12 cores for each biopsy course) and a negative (PI-RADSv.2 <3) or contraindications for mpMRI were the nested cases. The 11C-choline was synthesized using a General Electric TracerLab FXc module and administered in a total activity of 250-400 MBq. Total-body images were obtained with a PET/CT Discovery 690 (GE Healthcare) and acquired using an automated dose modulation (maximal 140 mA, 140 kVp), 64x3.75 mm collimation, 3.75 mm slice thickness, 0.5s rotation time, pitch 0.984:1. Reconstructed images of the pelvis were obtained and displayed for reading on an OsiriX MD Imaging workstation. The Bio-Jet fusion system and software (D&K Technologies, Barum, Germany) were used. Biopsies, transrectal or transperineal according to lesion site, were performed with patients in the dorsal lithotomic position, under antibiotic prophylaxis and local anaesthesia, using 3D triplane transrectal ultrasound system (BK Medical, Analogic Ultrasound Group, Pro Focus, Transducer 8818, 6/9 MHz). The primary endpoint was to assess whether 11C-choline PET/CT was able to determine the presence and the topographical distribution of the tumour foci. Data were complemented by statistical analysis.

Results

Of 298 consecutive patients enrolled from April 2015 to September 2016, 14 (mean age 65.3±8.3 years; tPSA 12.7±3.9 ng/ml) were cases of interest and underwent. PET documented 26 suspect lesions. The uptake values of ROIs on were: mean SUVmax 5.43 (±1.45; range: 1.9-8.3), mean SUVbackground 3.34 (±0.57; range1.6-5.5), SUVratio to background 1.64 (±0,35; range 1.16-2.51). PET/TRUS fusion biopsy was feasible in all patients. PCa was detected in 6 patients (42.8%). Of 77 cores, 23 (29.8%) were positive. Four patients harboured a significant PCa (GS > 6). The mean extension (length in mm) of PCa was higher in GS>6 patients than GS=6 patients (10,4 mm versus 5.5). We found no significant difference in mean values for SUVmax and SUVratio between benign (BPH + prostatitis) and malignant lesions. Patients with benign lesions presented a mean SUVmax and SUVratio of 5.77 and 1.64; patients with PCa had a mean SUVmax and SUVratio of 4.81 and 1.38 (p> 0.05).

Conclusions

Our findings showed a relative low accuracy of 11C-choline PET for detection of PCa, although patients with an aggressive PCa (GS>6) had a higher, but not statistically significant, uptake. Further studies using more specific radiotracers (i.e. 68Ga-PSMA PET/CT Imaging) are mandatory before introduction of this technique into clinical practice.

Funding

None