68Ga-RM2 PET/MRI: feasibility and workflow review

2708 Objectives Conventional imaging techniques for primary and metastatic prostate cancer detection are limited in specificity and sensitivity. 68Ga-labeled DOTA-4-amino-1-carboxymethyl-piperidine-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (68Ga-RM2, formerly known as 68Ga-Bombesin or BAY86-7548) is a novel synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptors (GRPr). GRPr are highly overexpressed in prostate cancer. Simultaneous PET/MR combines high-resolution PET data with the soft tissue definition of MRI. We reviewed the feasibility of 68Ga-RM2 PET/MR imaging in patients with prostate cancer using the GE SIGNA PET/MR scanner, as well as the overall procedure workflow. Methods Participants were recruited and consented under an IRB approved research protocol. 68Ga-RM2 was produced using a 68Ge/68Ga E&Z generator and timed for delivery 45min after participant arrival. This allows time for consenting, procedure review, MR safety screening and IV line placement. Vitals were recorded prior to injection and at scan completion. Due to the added steps of whole body (WB) MR such as placing coils, respiratory bellows, and ear protection, patients were positioned 35min post-injection for a targeted PET acquisition start time of 45-60min post-injection. MR localizer sequences over 4 stations were used for PET bed positioning and prescription of MR sequences. PET is acquired from mid-thigh to vertex (to avoid bladder filling) for 6 beds (3-4min each). MR attenuation correction, T1-weighted, T2-weighted and DWI sequences are included in each bed. Additional DWI and T2-weighted prostate specific sequences are included in the WB prescription and careful placement of the pelvic bed over the prostate was a critical step, such that these MR sequences were centered over the prostate bed. The pelvic bed was acquired for 15min for the additional MR sequences. MR slice thickness and field of view were maintained for every PET bed to allow for pasting of images for WB PET/MR co-registration. Breath holds were utilized for MR sequences over the chest and abdomen. Upon PET completion, a high-resolution DISCO sequence was performed over the prostate bed with dynamic gadobutrol injection. Results 16 men (59-83 year-old; mean±SD: 69.9±7.3) were injected with 140.6-152.6 MBq (mean±SD: 147.6 ±5) of 68Ga-RM2 and imaged using the GE SIGNA PET/MR. The uptake time between injection and start of PET acquisition ranged 41-63 minutes (mean±SD: 48.9±6.2) and total scan time ranged 65-91minutes (mean±SD: 77.2±10.9). All scans resulted in images of diagnostic quality. Vital signs were stable in all patients and no adverse events were recorded. Conclusions:68Ga-RM2 provided diagnostic images in patients diagnosed with prostate cancer. Total scan times varied greatly between initial scans. Patients with prostatectomy did not initially receive dedicated prostate imaging. Also, 6 participants received additional delayed post-void PET/MRI over the pelvis. Issues being assessed include the need for improved scatter correction of PET data, evaluating the benefit of delayed pelvis PET/MR and determining whether patients with radical prostatectomy benefit from dedicated high-resolution MR imaging.