The Suitability of 18F-PSMA for the Selection of Patients for the ¹⁷⁷Lu-PSMA Therapy

• Areas of Interest:

  • Prostate

  • Theragnostics

Background: Since 2015, it is accumulated a wealth of experience in the use of ¹⁷⁷Lu-PSMA-617 for castration resistant prostate cancer (CRPC) treatment. In most studies, PET-CT data with ⁶⁸Ga-PSMA-11 are used to select patients for the therapy; to date, this is the standard. But 18F-PSMA-1007 has some advantages compared with ⁶⁸Ga-PSMA-11 such as it has longer half-life, lower positron energy and higher resolution, it is better for primary tumor visualization, and it is cheaper in large nuclear imaging centers. Unfortunately, 18F-PSMA-1007 has higher uptake in the liver compared with other PSMA-targeted PET tracers; therefore, liver metastases of CRPC with relatively low PSMA expression may be missed by 18F-PSMA-1007 PET-CT. We conducted a pilot study to assess predictive value of F-PSMA to following Lu-177 therapy and imaging.

Methods: Four patients with 18F-PSMA-1007 positive lesions received minimal (diagnostic) activity of ¹⁷⁷Lu-PSMA-617 (0.4–0.9 GBq) and seven other patients received therapeutic activity of ¹⁷⁷Lu-PSMA-617 (up to 8 GBq). PET-CT data were compared with SPECT-CT 24 hours after ¹⁷⁷Lu-PSMA-617 administration. The patients had bone metastases and lymph node metastases, two patients had visceral metastases, one had metastases in the lungs and the other in liver.

Results: In all cases, we could see acceptable ¹⁷⁷Lu-PSMA-617 uptake in all metastatic lesions detected with the previous 18F-PSMA-1007 PET scan, no additional lesions were detected. There was no direct relationship between the intensity of ¹⁷⁷Lu-PSMA-617 uptake and SUV of 18F-PSMA-1007 PET-CT which may be due to significant differences in the dosage of lutetium.

Conclusion: 18F-PSMA-1007 PET-CT can be used as theranostic pare for the ¹⁷⁷Lu-PSMA-617. As for liver metastases, it is need for further investigation.

Publication History

Article published online:
10 May 2022