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Comparative Study
. 2014 Jan;41(1):11-20.
doi: 10.1007/s00259-013-2525-5. Epub 2013 Sep 27.

Comparison of PET imaging with a (68)Ga-labelled PSMA ligand and (18)F-choline-based PET/CT for the diagnosis of recurrent prostate cancer

Affiliations
Comparative Study

Comparison of PET imaging with a (68)Ga-labelled PSMA ligand and (18)F-choline-based PET/CT for the diagnosis of recurrent prostate cancer

Ali Afshar-Oromieh et al. Eur J Nucl Med Mol Imaging. 2014 Jan.

Abstract

Purpose: Positron emission tomography (PET) with choline tracers has found widespread use for the diagnosis of prostate cancer (PC). However, choline metabolism is not increased in a considerable number of cases, whereas prostate-specific membrane antigen (PSMA) is overexpressed in most PCs. Therefore, a (68)Ga-labelled PSMA ligand could be superior to choline tracers by obtaining a high contrast. The aim of this study was to compare such a novel tracer with standard choline-based PET/CT.

Methods: Thirty-seven patients with biochemical relapse of PC [mean prostate-specific antigen (PSA) 11.1 ± 24.1 ng/ml, range 0.01-116] were retrospectively analysed after (18)F-fluoromethylcholine and (68)Ga-PSMA PET/CT within a time window of 30 days. Radiotracer uptake that was visually considered as PC was semi-quantitatively analysed by measuring the maximum standardized uptake values (SUVmax) of the scans acquired 1 h after injection of (68)Ga-PSMA complex solution (median 132 MBq, range 59-263 MBq) and (18)F-fluoromethylcholine (median 237 MBq, range 114-374 MBq), respectively. In addition, tumour to background ratios were calculated.

Results: A total of 78 lesions characteristic for PC were detected in 32 patients using (68)Ga-PSMA PET/CT and 56 lesions were detected in 26 patients using choline PET/CT. The higher detection rate in (68)Ga-PSMA PET/CT was statistically significant (p=0.04). In five patients no lesion was found with both methods. All lesions detected by (18)F-fluoromethylcholine PET/CT were also seen by (68)Ga-PSMA PET/CT. In (68)Ga-PSMA PET/CT SUVmax was clearly (>10 %) higher in 62 of 78 lesions (79.1 %) and the tumour to background ratio was clearly (>10 %) higher in 74 of 78 lesions (94.9 %) when compared to (18)F-fluoromethylcholine PET/CT.

Conclusion: (68)Ga-PSMA PET/CT can detect lesions characteristic for PC with improved contrast when compared to standard (18)F-fluoromethylcholine PET/CT, especially at low PSA levels.

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Figures

Fig. 1
Fig. 1
SUVmax (a) of all 78 lesions characteristic for PC and their ratio to background SUVmax (= contrast, b) 1 h post-injection in both 68Ga-PSMA PET/CT (left columns) and 18F-fluoromethylcholine PET/CT (right columns). Green columns indicate lymph node metastases, blue columns local relapses, grey columns bone metastases and red columns soft tissue metastases
Fig. 2
Fig. 2
Patient 12 (a, b) and patient 18 (c, d). Red arrows point to a nodular pelvic wall metastasis (a, b, histologically confirmed) and to small lymph nodes (c, d) which present with clearly pathological tracer uptake in 68Ga-PSMA PET/CT (b and d) only. Yellow arrows point to both catheterized ureters (c, d). Patient 12 presented with a minimal PSA value (0.01 ng/ml) despite visible tumour lesions. The PSMA ligand is therefore able to detect low differentiated PC. a + c Fusion of 18F-fluoromethylcholine PET and CT, b + d fusion of 68Ga-PSMA PET and CT. Colour scales as automatically produced by the PET/CT machine
Fig. 3
Fig. 3
Patient 13 (a, b) and patient 18 (c, d). Red arrow in b points to a liver metastasis (histologically confirmed, lesion 16 in Fig. 1) visible only in 68Ga-PSMA PET/CT due to relatively low background activity when compared to 18F-fluoromethylcholine PET. In d, red arrow points to a lymph node which presents with clearly pathological tracer uptake in 68Ga-PSMA PET/CT despite a beam hardening artefact (lesion 28 in Fig. 1). In 18F-fluoromethylcholine PET/CT, however, there is no pathological uptake (c). a + c Fusion of 18F-fluoromethylcholine PET and CT, b + d fusion of 68Ga-PSMA PET and CT. Colour scales as automatically produced by the PET/CT machine
Fig. 4
Fig. 4
Patient 15. Red arrow points to a vertebral metastasis visible in 68Ga-PSMA PET/CT (a) only. Due to physiological high background activity in the vertebral column, vertebral metastases are usually difficult to detect in choline PET (c). Typical for choline PET is also a frequently high background activity as visible in the maximum intensity projection (MIP, d). Image data are given as automatically produced by the PET/CT machine to demonstrate that the filtering of the MIPs was equally set. Although it appears that the automatically set scales may not be optimal to detect lesions on the MIP in every case (e.g. lesion in b is better visualized on the workstation than in this figure), we preferred to avoid changes of all figures presented in this study. a Fusion of 68Ga-PSMA PET and CT, b MIP of 68Ga-PSMA PET, c fusion of 18F-fluoromethylcholine PET and CT, d MIP of 18F-fluoromethylcholine PET. Colour scales as automatically produced by the PET/CT machine

Comment in

  • Writing PET into existence.
    Chiti A, Kirienko M, Incerti E, Picchio M. Chiti A, et al. Eur J Nucl Med Mol Imaging. 2014 Jan;41(1):7-10. doi: 10.1007/s00259-013-2573-x. Epub 2013 Sep 27. Eur J Nucl Med Mol Imaging. 2014. PMID: 24072349 No abstract available.

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