Abstract: Background and purpose: The data of radioactive imaging drug dose distribution in human body, absorbed dose of organs and effective dose of whole body are very important. The purpose of this study was to estimate the absorbed doses of different organs and the effective dose from the biodistribution of the  ^99m Tc-hydrazinonicotinyl-Tyr3-octreotide ( ^99m Tc-HYNIC-TOC) in humans with hybrid single photon emission computed tomography (SPECT) imaging. Methods: Whole body planar imaging was acquired at 0.5, 1.0, 2.0, 4.0 and 8.0 h after administration of 370 MBq  ^99m Tc-HYNIC-TOC to 5 patients with neuroendocrine tumors who were treated in Fudan University Shanghai Cancer Center from May to Jun. 2018, and the tomography of the whole body was achieved at 2.0 h. After iterative reconstruction, the data were imported into GE Dosimetry Toolkit. Region of interest (ROI) of different organs was delineated in SPECT/CT images, and the residence time equal to the area under the curve was calculated by time-activity curve. The absorbed doses of different organs and the whole body and the effective dose of whole body were calculated by OLINDA/EXM software according to the standard methods which were developed by Medical Internal Radiation Dose (MIRD) Committee. Results: The absorbed dose coefficients of spleen, bladder and kidney (adult male: 0.042, 0.019 and 0.016 mGy/MBq; adult female: 0.026, 0.027 and 0.019 mGy/MBq) were much higher than those of brain, skin and thyroid (adult male: 0.000 3, 0.000 5 and 0.000 5 mGy/MBq; adult female: 0.000 3, 0.000 5 and 0.000 6 mGy/MBq). The range of absorbed dose coefficients of radiosensitive organs such as osteogenic cells, thymus and red marrow was 0.001 2-0.002 2 mGy/MBq. The absorbed dose coefficient of whole body was 0.001 7 mGy/MBq for adult male and 0.001 6 mGy/MBq for adult female. The effective dose coefficient of whole body was 0.004 58 mSv/MBq for adult male and 0.004 55 mSv/MBq for adult female. Conclusion:  ^99m Tc-HYNIC-TOC is feasible to be used safely in human beings because the effective dose of whole body is lower than dose constraining. This study can provide the basis for using  ^99m Tc-HYNIC-TOC safely in the clinical practice.

Key words:  ^99m Tc-Hydrazinonicotinyl-Tyr3-Octreotide, Biodistribution, Medical Internal Radiation Dose methods, Human absorbed dose