Presentation Authors: Georges Mehawed*, Paria Saadat, Michelle Ong, Andre Joshi, Matthew Roberts, Marlon Perera, Handoo Rhee, Alex Yeates, Ian McKenzie, Janelle Munns, Greg Malone, Eric Chung, Peter Heathcote, John Preston, Malcolm Lawson, Simon Wood, Sonja Gustafson, Kenneth Miles, Stanley Ngai, Ian Vela, Brisbane, Australia
Introduction: Hybrid (68) Ga-labelled Prostate Specific Membrane Antigen (PSMA) positron emission tomography (PET) with magnetic resonance imaging (MRI) serves to combine detailed resolution of MRI with whole body molecular tumour localisation to improve sensitivity and specificity for metastasis detection during primary staging of prostate cancer. Reports on hybrid PSMA PET/MRI are limited, hence we sought to evaluate the utilisation and diagnostic accuracy within a large series from our institution.
Methods: A retrospective review of all PSMA PET/MRI studies performed in our tertiary referral institution between April 2015 to April 2017 was conducted. Indications for scans, PSA levels, findings of positive scans including lymph nodes, bone and soft tissue, detection rate, prior histology and further treatment was reviewed.
Results: Of 300 PSMA PET/MRI studies performed, 115 studies were for primary staging purposes prior to therapy of curative intent in high risk prostate cancer. 106 studies demonstrated uptake within the prostate and soft tissue. The proportion of patients with PSMA avid lesion Gleason score of 8 or above was 37.7% while the median PSA level at the time of scan was 15 ng/ml. 105 (91%) of these scans demonstrated uptake in the primary prostate tumor, of which 66 were localized to only to the prostate. 39 diagnosed with additional extra-prostatic disease with 13 cases having only bone lesions,15 cases with only lymph node positive disease and 3 patients with soft tissue disease, such as lung or urethra. 8 cases had mixed disease. Among tumours without PSMA avidity, one patient had a Gleason score of 9, others had a Gleason score of 7. Median PSA in this group was 6.9 ng/ml.
Conclusions: The use of PSMA PET/MRI in primary staging of high risk prostate cancer appears promising. PSMA PET/MRI had a high detection rate of 92.1% of avid prostatic lesions in our cohort including a 34% metastatic rate. In the staging setting, this modality could be used to assist in therapeutic planning, and can potentially reduce the need for multiple imaging modalities in preparation for curative treatment of patients with prostate cancer.