Accuracy of lymph node imaging in prostate cancer: a prospective cohort study to determine the concordance between ⁶⁸ Ga-PSMA-PET-CT and ferumoxtran-10 magnetic resonance imaging (nano-MRI)

Ziel/Aim To prospectively determine the combined value of ⁶⁸Ga-PSMA-PET/CT and nano-MRI to detect lymph node metastases in patients with prostate cancer at intermediate to high risk with extended pelvic node dissection (e-PLND) as ‘gold standard’.

Methodik/Methods 42 patients with intermediate/high risk prostate cancer underwent pre-operative ⁶⁸Ga-PSMA-PET-CT and nano-MRI. For nano-MRI, Ultra Small Iron Oxide Particles (USPIO, Ferrotran/Sinerem/Combidex) [1] was used. Two months after prostatectomy and e-PLND a non-contrast pelvic MRI was performed to determine which pre-operatively imaging-positive lymph nodes (+LNs) were removed. Level of Suspicion (LOS) scorings (from 1=benign to 5=malignant) for +LNs on PSMA-scan and/or nano-MRI were given by a joint reading of nuclear medicine specialist and radiologist. Imaging results were compared with e-PLND-pathology results.

Ergebnisse/Results 108 LNs with LOS>3 were identified on nano-MRI and/or PSMA scans. Only 14 % (15/108) of these +LNs were removed with e-PLND and could be pathologically evaluated. Of these 15 +LNs nano-MRI correctly identified 86 % (13/15) and PSMA-scan 33 % (5/15), respectively. The percentage of detected +LNs <3.5mm were 69 % (9/13) and 40 % (2/5) for nano-MRI and PSMA-scans, respectively. False positive rate was 6.6 % for both imaging techniques. On patient level 36 % (15/42) were positive for +LNs. Nano-MRI and PSMA-scan detected 100 % (15/15) and 60 % (9/15) of patients, respectively.

Schlussfolgerungen/Conclusions With e-PLND only 14 % of +LNs were removed, showing the limitation of the ‘gold-standard’. In agreement with literature nano-(USPIO)-MRI detected more positive LNs with smaller diameter (<3.5mm)¹ compared to ⁶⁸Ga-PSMA-PET-CT. The missed +LNs were predominantly at a size which is at the edge or below the physical scanner-resolution.

• Literatur/References

• 1 Heesakkers R. et al. MRI with a lymph-node-specific contrast agent as an alternative to CT scan and lymph-node dissection in patients with prostate cancer: A prospective multicohort study. Lancet Oncology, 2008; 9 : 859-856.