Head-to-head comparison of ⁶⁸Ga-prostate-specific membrane antigen PET/CT and ferumoxtran-10 enhanced MRI for the diagnosis of lymph node metastases in prostate cancer patients

Abstract

Accurate assessment of lymph node (LN) metastases in prostate cancer (PCa) patients is critical for prognosis and patient management. Both prostate-specific membrane antigen- (PSMA) positron emission tomography/computed tomography (PET/CT) and ferumoxtran-10 nanoparticle-enhanced magnetic resonance imaging (nano-MRI) are imaging modalities with high potential to identify LN metastases in PCa patients. The aim of this study is to compare the results of those imaging technologies in terms of characteristics and anatomical localisation of suspicious LNs in order to assess the feasibility of their complementary use for imaging in PCa patients. Methods: A total of 45 patients with either primary PCa (n = 8) or recurrence (n = 36) were included in this retrospective study. All patients underwent both PSMA-PET/CT and nano-MRI between October 2015 and July 2017 within a time frame of three weeks. Both scans were performed at the same institution according to local clinical protocols. All scans were analysed independently by experienced nuclear medicine physicians and radiologists. The size, anatomical location and Level of Suspicion (LoS) were determined for all visible LNs. Subsequently, the findings from PSMA-PET/CT and nano-MRI were compared, irrespective to a reference standard. Results: 179 suspicious LNs were identified. Significantly more suspicious LNs per patient were detected by nano-MRI (p<0.001): 160 were identified in 33 patients by nano-MRI, versus 71 in 25 patients by PSMA-PET/CT. Of all suspicious LNs 108 were only identified by nano-MRI (60%), 19 (11%) were detected only by PSMA-PET/CT, and 52 (29%) were found by both methods. The mean size of the suspicious LNs as identified by nano-MRI was significantly smaller (5.3mm) than those detected by PSMA-PET/CT (6.0mm; P = 0.006). Median LoS did not differ significantly. Both modalities identified suspicious LNs in all anatomical regions of the pelvis. Conclusion: Both modalities identified suspicious LNs which were missed by the other. Both modalities identified suspicious LNs in all anatomical regions of the pelvis, however nano-MRI appeared to be superior in detecting smaller suspicious LNs. These findings suggest a potential complemental role for nano-MRI to PSMA-PET/CT, however, since the clinical implications of the different results are not well established yet, further investigation in this complementary use is encouraged.