Preliminary Results of an Ongoing Prospective Clinical Trial on the Use of 68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI in Staging of High-Risk Prostate Cancer Patients

Abstract

The aim of the present study is to investigate the synergic role of 68Ga-PSMA PET/MRI and 68Ga-DOTA-RM2 PET/MRI in prostate cancer (PCa) staging. We present pilot data on twenty-two patients with biopsy-proven PCa that underwent 68Ga-PSMA PET/MRI for staging purposes, with 19/22 also undergoing 68Gaa-DOTA-RM2 PET/MRI. TNM classification based on image findings was performed and quantitative imaging parameters were collected for each scan. Furthermore, twelve patients underwent radical prostatectomy with the availability of histological data that were used as the gold standard to validate intraprostatic findings. A DICE score between regions of interest manually segmented on the primary tumour on 68Ga-PSMA PET, 68Ga-DOTA-RM2 PET and on T2 MRI was computed. All imaging modalities detected the primary PCa in 18/19 patients, with 68Ga-DOTA-RM2 PET not detecting any lesion in 1/19 patients. In the remaining patients, 68Ga-PSMA and MRI were concordant. Seven patients presented seminal vesicles involvement on MRI, with two of these being also detected by 68Ga-PSMA, and 68Ga-DOTA-RM2 PET being negative. Regarding extraprostatic disease, 68Ga-PSMA PET, 68Ga-DOTA-RM2 PET and MRI resulted positive in seven, four and five patients at lymph-nodal level, respectively, and at a bone level in three, zero and one patients, respectively. These preliminary results suggest the potential complementary role of 68Ga-PSMA PET, 68Ga-DOTA-RM2 PET and MRI in PCa characterization during the staging phase.

68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI in Recurrent Prostate Cancer: Diagnostic Performance and Association with Clinical and Histopathological Data

“…So far, only few studies have investigated the combined use of both 68 Ga-PSMA and 68 Ga-DOTA-RM2 PET in PCa both in the staging and restaging setting, using PET/MRI and PET/CT alternatively [ 10 , 12 , 13 , 14 ].…”

“…For this reason, GRPR analogues have been recently identified as alterative targets for molecular imaging in prostate cancer [ 8 ]. So far, among the available radiotracers targeting GRPR, 68 Ga-DOTA-RM2 has been the most investigated [ 9 , 10 , 11 , 12 ].…”

“…Very few studies have been reported on the combined use of both 68 Ga-PSMA and 68 Ga-DOTA-RM2 in prostate cancer setting, both in the staging [ 12 , 13 ] and restaging [ 10 , 14 ] phase of the disease, with the majority of them using PET/computed tomography (CT) scanners for imaging acquisition [ 10 , 13 , 14 ].…”

“…However, very limited data are currently available on its role in this specific clinical setting. In particular, studies using both 68 Ga-PSMA and 68 Ga-DOTA-RM2 with PET/MRI are still anecdotal [ 10 , 12 , 14 ]…”

Radiolabeled PSMA Inhibitors

“…A recent preclinical study, which evaluated retrospectively frozen prostatectomy samples ( n = 20) with tissular microimaging using [ 111 In]In-PSMA-617 and the GRPr antagonist [ 111 In]In-RM2 ([ 111 In]In-DOTA-4-amino-1-carboxymethyl-piperidine- D -Phe 6 -Gln 7 -Trp 8 -Ala 9 -Val 10 -Gly 11 -His 12 -Sta 13 -Leu 14 -NH 2 ), showed that for [ 111 In]In-PSMA-617 the binding was high and independent of the metastatic risk ( p = 0.665), Gleason score ( p = 0.555), or PSA value ( p = 0.404), while [ 111 In]In-RM2 exhibited a significantly higher binding in the low metastatic risk group ( p = 0.046), in the low PSA value group ( p = 0.001), and in samples with Gleason 6 score ( p = 0.006) [ 162 ]. A limited number of patients have been screened with a PSMA-targeting imaging agent ([ 68 Ga]Ga-PSMA-11 or [ 18 F]DCFPyL) and the GRPr antagonist [ 68 Ga]Ga-RM2 [ 163 , 164 , 165 , 166 , 167 ] resulting rather in a complementing than in a competing approach of PSMA vs. GRPr imaging [ 165 , 168 ].…”