Intraoperative somatostatin receptor detection after peptide receptor radionuclide therapy with ¹⁷⁷Lu-and ⁹⁰Y-DOTATOC (Tandem PRRNT) in a patient with a metastatic neuroendocrine tumor

Aim: The aim of this chapter is to present the results of the first intraoperative somatostatin receptor detection after peptide receptor radionuclide therapy (PRRNT) with ⁹⁰Y- and ¹⁷⁷Lu-DOTATOC using a handheld gamma probe and comparison with the findings of preoperative ⁶⁸Ga-DOTATOC PET/CT in a patient with a metastatic neuroendocrine tumor (NET) of the ileum. Materials and Methods: A 56-year-old female patient, treated twice by PRRNT, was admitted for the third cycle and subsequent surgery. Before operation, the following studies were performed for restaging after the second cycle of PRRNT: ^99mTc-MAG3 + TER, ^99mTc-DTPA + GFR, abdominal ultrasonography, MRI of the abdomen, ⁶⁸Ga-DOTATOC PET/CT as well as ¹⁸F-fluoride PET/CT. Serum tumor markers were measured before and after PRRNT. Tandem PRRNT was performed using 3000 MBq ⁹⁰Y-DOTATOC and 6000 MBq ¹⁷⁷Lu-DOTATOC. Whole-body scintigrams were obtained at 23 and 43 h. Five days after PRRNT, the patient was operated using a handheld gamma probe. Immunohistochemistry and histopathology of the resected tissue were performed. Results: Tandem PRRNT was very well tolerated by the patient. Before PRRNT, ⁶⁸Ga-DOTATOC PET/CT revealed the primary tumor in the ileocoecal region as well as bilobular liver metastases and a right iliac bone lesion (osteoblastic on ¹⁸F-fluoride PET/CT). Compared with the previous findings, there was good therapy response (partial remission of the tumor lesions). No nephrotoxicity was observed. Serum chromogranin A (836 μg/l, n < 100) and serotonin (852 μg/l, n < 200) were strongly elevated. Posttherapy scans showed intense uptake in metastases and the primary tumor. Intraoperative gamma probe detectedin addition to the known lesionsbilateral ovarian metastases not visualized by ⁶⁸Ga- DOTATOC PET/CT. Bilateral adnexectomy, right hemicolectomy, excision of hepatic metastases in S3, and partial resection of peritoneum were performed. Histopathology confirmed metastases in both ovaries. Conclusions: Gamma probe-guided surgery after ¹⁷⁷Lu PRRNT is feasible and appears to be more sensitive than ⁶⁸Ga-DOTATOC PET/CT. This technique might aid the surgeon in achieving more complete tumor resection through intraoperative detection of very small lesions (<5 mm) directly after PRRNT.