Dosimetry of 177Lu-DOTATOC First Circle Treatment in Patients With Advanced Metastatic Neuroendocrine Tumors: a Pilot Study in China

Objective: The aim of this study was to calculate the dosimetry of 177 Lu-DOTATOC in the first circle of peptide receptor radionuclide treatment (PRRT) in patients with advanced neuroendocrine tumors (NETs). Patients and Methods: Eight patients (4 female, 4 male) with NETs were enrolled in this study. All these patients with unresectable primary lesion and multiple metastasis received 177 Lu-DOTATOC treatment with a single activity of 1.59-3.49 GBq (43.1-94.2 mCi) and underwent a series of whole-body planar scan at 0.5 h, 24 h, 48 h and 72 h and SPECT/CT scan at 24 h after injection. The region of interest (ROI) was drawn on the primary and metastatic lesion, the mediastinum served as control area. Therefore, the ratio of tumor-to-mediastinum (T/NT) was also calculated. The Hermes hybrid viewer dosimetry module together with OLINDA/EXM 2.0 was used to determine absorbed doses of organs and tumors. Results: : No significant changes in both laboratory test was found after 177 Lu-DOTATOC treatment, including renal function and blood cell analysis ( F= 0.047-1.062, P =0.364-0.959). Physiological uptake of 177 Lu-DOTATOC was seen in the liver, the spleen and the kidneys. Focal uptake of 177 Lu-DOTATOC was found in the tumors including primary tumors and metastatic lesions, the ratio of T/NT was 39.45 ± 28.83. The residence time of 177 Lu-DOTATOC was 0.82 ± 0.12 h for left kidney, 0.80 ± 0.15 h for right kidney, 1.35 ± 0.89 h for spleen, 1.80± 2.70 h for tumors, and 30.21 ± 11.29 h for total body. Organs with the highest absorbed doses per injected activity were tumors (1.2936 ± 0.8625 mGy/MBq), spleen (0.4608 ± 0.4084 mGy/MBq), and kidneys (0.3843 ± 0.1120 mGy/MBq). The mean effective dose was 0.0392 ± 0.0158 mSv/MBq with the range of 0.0158-0.0674 mSv/MBq. In addition, Photon cross-irradiation was found to reach 19.46 % in adrenals, whereas photon can contribute less than 3% of the kidneys’ total dose. Conclusion: This study demonstrates that absorbed dose in the kidneys and spleen are relatively lower, whereas the tumor shows longer retention time and higher internal radiation absorbed dose in PRRT. PRRT is a well-tolerated treatment strategy. 177 Lu-DOTATOC SPECT /CT serves as independent predictor for the evaluation of response to PRRT, which contributes to predict the response to PRRT and the related adversity.