OBJECTIVES

A broad pool of radionuclides becomes available for labelling of the prostate-specific membrane antigen (PSMA) inhibitor, Glu-NH-CO-NH-Lys (Ahx), when using DOTA as chelator. Recently the novel DOTA based PSMA-617 has shown great results in prostate cancer therapy and PET imaging when labelled with ¹⁷⁷Lu and ⁶⁸Ga. Do to the short half-life of ⁶⁸Ga, long acquisition periods cannot be acquired. In this context, ⁴⁴Sc with a half-life of 3.97 h and suitable decay characteristics for PET imaging, is an alternative to ⁶⁸Ga. In this study, ⁴⁴Sc-labelled PSMA-617 was evaluated in a first human application for pre-therapeutic dosimetry of prostate cancer.

METHODS

PSMA-617 was obtained from ABX (Radeberg, Germany). ⁴⁴Sc was obtained from a ⁴⁴Ti/⁴⁴Sc generator in Mainz, where ⁴⁴Ti decays with a half-life of 60 d to no-carrier-added (n.c.a) ⁴⁴Sc. Radiolabeling with ⁴⁴Sc and quality control was performed according to legal regulations. Dynamic PET data was acquired 30 min after bolus injection over one bedposition including the kidneys, followed by one static whole body acquisition at 30, 120 and about 1200 minutes p.i.. Veneous blood samples were drawn 1, 3, 5, 10, 15, 20, 25, 30, 120, and about 1200 minutes p.i..

RESULTS

All ⁴⁴Sc-PET images had similar or better diagnostic capability than ⁶⁸Ga-PSMA images. Contrast to background ratio was even better in some metastases in ⁴⁴Sc-images. In the late image hardly any tracer accumulation in the kidneys was found while the lacrimal and salvatory glands stilled showed relevant uptake. Therefore ⁴⁴Sc-based dosimetry will show probably lower absorbed dose for the kidneys and higher absorbed dose for the lacrimal and salvatory glands than ⁶⁸Ga-based dosimetry, being more accurate due to the longer measurement times.

CONCLUSIONS

This first evaluation of ⁴⁴Sc-PSMA-617 for pre-therapeutic dosimetry demonstrate the great potential of ⁴⁴Sc as PET nuclide.