Abstract
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Objectives: Recently, 18F-PSMA-1007 was proposed as technological advance compared to 68Ga-PSMA-11 enabling higher patient numbers from a single batch obtained by cyclotron-based production. A probable advantage of this novel tracer is its slightly more lipophilic profile leading to reduced bladder radioactivity compared to 68Ga-PSMA-11, beneficial for correct detection of pathologies in the prostatic fossa. Compared to PET/CT, PET/MRI has intrinsic advantages for assessment of the abdomen and prostatic fossa due to higher soft tissue contrast, demonstrated previously for 68Ga-PSMA-11, allowing for improved anatomical landmarking. We hypothesized that physiological and pathological biodistribution of 18F-PSMA-1007 is reproducibly depicted using PET/MRI compared to PET/CT while providing significantly higher anatomical detail in the pelvis in the MRI component.
Methods: The retrospective study was performed in agreement with the declaration of Helsinki. Five patients prior radical prostatectomy due to histophatologically confirmed prostate cancer and one patient with biochemical recurrence were scanned after receiving 18F-PSMA-1007. Prior to PET/MRI (3h p.i., Siemens Biograph mMR 3 Tesla, 4min/bed), a PET/CT (1h p.i., FlowMotion technology using Siemens mCT Flow) was performed. The PET/MRI protocol (Figure 1) included a novel CAIPIRINHA-accelerated attenuation correction prototype and axial T2w haste sequence allowing for fast high-resolution anatomical whole-body MRI sequences for MRI/PET fusion. A dedicated MRI protocol of the prostate fossa including high-resolution T2w-TSE sequences (axial, sagittal) orientation, axial contrast-enhanced T1w GRE dynamic (50 timepoints) and axial diffusion-weighted imaging (b0 and b1500 s/mm2) was included. The mpMRI protocol was simultaneously accompanied by a 9 min PET scan to allow perfect PET/MRI fusion with equal bladder filling in PET and MRI due to simultaneous acquisition followed by two high-resolution T1w-post-contrast VIBE sequences (axial/coronal) for whole-body imaging. Images were assessed in consensus by first and last author. We compared correlation between PET/CT and PET/MRI of patients including PET image quality and quantified standardized uptake values (SUVs) of tumor, liver, kidneys and bladder by using a 60% isocontour of SUVmax.
Results: Whole-body MRI with excellent image quality succeeded in all patients providing 6 whole-body sequences for anatomical landmarking. SUVmax and SUVmean of PET/CT and PET/MRI correlated significantly (r=0.91 and 0.94; p<0.0001, respectively; see Figure 2). Tumor SUVs demonstrated higher SUVs in 3h p.i. (PET/MRI) in 5 of 6 patients. The prostate cancer lesions could be detected by MRI as well, determined as PI-RADS 5 lesion. In two patients, extracapsular extension was detectable in MRI. One lymph node was PET-positive but negative in MRI and CT. In contrast to 68Ga-PSMA-11-PET/MRI, no halo artifacts surrounding the bladder were found. However, photopenic areas surrounding liver and kidneys were noticed in all patients but may be retrospectively corrected from PET raw data.
Conclusion: We present first patient data on the reproducible whole-body application of simultaneous 18F-PSMA-1007-PET/MRI. In particular, the combination of optimal pharmacodynamics of 18F-PSMA-1007 (low bladder signal) and the PI-RADS 2.0 compliant MRI protocol being standard for assessment of primary prostate cancer represent an optimal synergy of molecular and radiological assessment by exploiting the strengths of both to overcome limitations that each modality may have as single part. The present protocol allows patient- and dose-efficient whole-body PET/MRI scans in clinical routine in particular suited for high-risk patients with prostate cancer for which local as well as distant staging is demanded in one single step. Research Support: . $$graphic_A1610367-94DF-4C31-AEAB-8904B9116B03$$ $$graphic_DC1F631F-BAC5-4A17-A1F4-FE8415A88CBB$$
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