B. Frisch, T. Maurer, A. Okur, T. Weineisen, , H. Kübler, N. Navab, HP Wester, M. Schwaiger, M. Eiber Freehand SPECT for 111In-PSMA-I&T radioguided lymphadenectomy in prostate cancer patients Society of Nucler Medicine and Medical Imaging Annual Meeting, Baltimore, USA, 2015 (bib)
	Objectives : Ga-HBED-PSMA (Prostate Specific Membrane Antigen) PET combined with multiparametric MR allows for the preoperative visualization of even small and atypically localized metastatic lesions of PSMA-overexpressing prostate cancer (PCa). The challenge lies in the intraoperative identification of these lesions. This work evaluates the feasibility of radioguided surgery (RGS), using freehand SPECT (fhSPECT) to localize metastatic lesions after the injection of In-PSMA I&T. Methods : 5 PCa patients with evidence of lymph node metastases on Ga-HBED-PSMA PET/MR were included in this study. They were injected with In-PSMA I&T 24 hours before surgery. Intraoperatively, fhSPECT uses a gamma probe whose read-out is recorded together with its position and orientation to reconstruct a live 3D image of the radioactivity distribution. Ex vivo measurements by gamma probe and histological analysis served as reference standard. Results : Samples identified to be radioactive during surgery were confirmed to have increased radioactivity ex-vivo and proved to be metastatic PCa by histopathology. In total, 28 specimens were histologically evaluated, out of which 15 contained metastatic lesions. No non-radioactive sample contained metastatic tissue. In 2 patients, PSMA-RGS allowed the identification of additional lesions as compared to Ga-PSMA PET/MR. Conclusions : In this intial study, intraoperative imaging with the fhSPECT technique proved to be feasible and enabled intraoperative identification of PCa metastases in lymph nodes using In-PSMA I&T. Further studies including greater patient cohorts and follow-up are required to evaluate the benefits of intraoperative In-PSMA I&T based lymph node detection and fhSPECT in clinical routine.
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