SIU 2017: Comparison of 68Ga-PSMA-PETCT with Multiparametric MRI for Staging High Risk Prostate Cancer

Lisbon, Portugal ( Glu-NH-CO-NH-Lys(Ahx) Ga-68(HBED-CC))) (Ga-68 PSMA 11) is a positron emission tomography (PET) imaging agent that is increasingly being evaluated in prostate cancer. It is used for staging of prostate cancer, localizing recurrence in patients with biochemical relapse and finding metastases in patients with castration resistant prostate cancer. In this study the authors attempted to compare Ga-68 PSMA 11 PET/CT with multiparametric MRI for the staging of high risk prostate cancer.

From Jan 2015 to October 2016, 36 patients with high-risk prostate cancer were included. All patients included in this study had biopsy proven prostate cancer with a serum PSA >20 and/or Gleason's Score >8. Each patient underwent both Ga-68PSMA-PET-CT and multiparametric MRI within one week. Both modalities were compared in terms of staging of the primary disease, lymph node and bone involvement. The prostate gland was divided into twelve segments. The segment with the highest SUVmax and lowest ADC value was regarded as the primary site. Concordance between this primary and uptake on Ga-68PSMA-PET-CT was checked. Concordance was also checked for extension into seminal vesicle(s), regional and systemic lymph nodes, skeletal sites, liver and lungs.

Median age was 65 years (range: 44-80 years), median PSA was 94.3 ng/ml (range 20-19005 ng/ml). Concordance for localization of primary lesion on Ga-68PSMA-PET-CT & MRI was seen in 19/36 (52.7%). PET was incorrect for seminal vesicle involvement in 8 patients. Capsular involvement could not be commented upon on PET. T staging on Ga-68-PSMA-PET-CT and MRI was similar in 21/36 patients (58.3%) and differed in 15/36 patients (41.7%). Ga-68 PSMA PET/CT detected higher number of patients with regional (29) and non-regional (15) lymph nodes in comparison to MRI (20 and 5 respectively). Concordance for regional lymph node staging was seen in 25 patients (69.4%) and for non-regional lymph node staging in 26 patients (72.2%). In one patient Ga-68-PSMA-PET-CT reported skeletal metastases which was not seen on MRI. Ga-68-PSMA-PET-CT detected distant metastases involving lung (2 patients) and liver (1 patient) not seen on MRI. In comparison to MRI, Ga-68-PSMA-PET-CT changed M stage from MO to Mla in one patient, from MO to M1b in 1 patient and from M1b to M1c in 3 patients.

In conclusion, when compared to MRI, Ga-68 PSMA PET/CT was able to detect more lymph node involvement (both regional and non-regional) as well as metastases. It was also useful for localization of primary however concordance for primary localization with MRI was limited and so was the depiction of capsular invasion and seminal vesicle involvement.

Presented by: Seth A 
Affiliation: All India Institute of Medical Sciences, New Delhi, India

Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre.Twitter: @GoldbergHanan at the 37th Congress of Société Internationale d’Urologie - October 19-22, 2017- Lisbon, Portugal

email news signup