The (68)Ga/(177)Lu theragnostic concept in PSMA targeting of castration-resistant prostate cancer: correlation of SUVmax values and absorbed dose estimates

A targeted theragnostic approach based on increased expression of prostate-specific membrane antigen (PSMA) on PC cells is an attractive treatment option for patients with metastatic castration-resistant prostate cancer (mCRPC).

Ten consecutive mCRPC patients were selected for (177)Lu-PSMA617 therapy on the basis of PSMA-targeted (68)Ga-PSMA-HBED-CC PET/CT diagnosis showing extensive and progressive tumour load. Following dosimetry along with the first therapy cycle restaging ((68)Ga-PSMA-HBED-CC and (18)F-NaF PET/CT) was performed after 2 and 3 therapy cycles (each 6.1 ± 0.3 GBq, range 5.4-6.5 GBq) given intravenously over 30 minutes, 9 ± 1 weeks apart. PET/CT scans were compared to (177)Lu-PSMA617 24-hour whole-body scans and contrast-enhanced dual-phase CT. Detailed comparison of SUVmax values and absorbed tumour doses was performed.

(177)Lu-PSMA617 dosimetry indicated high tumour doses for skeletal (3.4 ± 1.9 Gy/GBq; range 1.1-7.2 Gy/GBq), lymph node (2.6 ± 0.4 Gy/GBq; range 2.3-2.9 Gy/GBq) as well as liver (2.4 ± 0.8 Gy/GBq; range 1.7-3.3 Gy/GBq) metastases whereas the dose for tissues/organs was acceptable in all patients for an intention-to-treat activity of 18 ± 0.3 GBq. Three patients showed partial remission, three mixed response, one stable and three progressive disease. Decreased (177)Lu-PSMA617 and (68)Ga-PSMA-HBED-CC uptake (mean SUVmax values 20.2 before and 15.0 after 2 cycles and 11.5 after 3 cycles, p < 0.05) was found in 41/54 skeletal lesions, 12/13 lymph node metastases, 3/5 visceral metastases and 4/4 primary PC lesions.

Due to substantial individual variance, dosimetry is mandatory for a patient-specific approach following (177)Lu-PSMA617 therapy. Higher activities and/or shorter treatment intervals should be applied in a larger prospective study.

European journal of nuclear medicine and molecular imaging. 2017 Jan 12 [Epub ahead of print]

Lorenza Scarpa, Sabine Buxbaum, Dorota Kendler, Katharina Fink, Jasmin Bektic, Leonhard Gruber, Clemens Decristoforo, Christian Uprimny, Peter Lukas, Wolfgang Horninger, Irene Virgolini

Department of Nuclear Medicine, Medical University Innsbruck, Anichstra├če 35, A-6020, Innsbruck, Austria., Department of Urology, Medical University of Innsbruck, Innsbruck, Austria., Department of Radiology, Medical University of Innsbruck, Innsbruck, Austria., Department of Radiotherapy / Radiation Oncology, Medical University of Innsbruck, Innsbruck, Austria., Department of Nuclear Medicine, Medical University Innsbruck, Anichstra├če 35, A-6020, Innsbruck, Austria. .

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