Equivalent dose rate at 1m of patients with known or suspected neuroendocrine tumor exiting a nuclear medicine department after ⁶⁸Ga-DOTATOC, ¹⁸F-FDOPA or ¹⁸F-FDG PET/CT, or ¹¹¹In-pentetreotide or ¹²³I-mIBG SPECT/CT

Abstract

¹²³I-mIBG and ¹¹¹In-pentetrotide SPECT have been used for functional imaging of neuroendocrine tumors (NET) for the last two decades. More recently, PET/CT imaging with ¹⁸F-FDG, ¹⁸F-FDOPA and ⁶⁸Ga somatostatin-receptor ligands in NETs has been expanding. No direct measurements of the dose rate from NET patients exiting the nuclear medicine department could be found in the literature after PET/CT with ¹⁸F-FDOPA or ⁶⁸Ga-DOTATOC, a somatostatin analogue. Methods: We measured the dose rates from NET patients undergoing PET/CT or SPECT/CT in our centers. A total of 103 paired measurements of equivalent dose rate at 1m of the patient (EDR-1m) were performed in 98 patients on leaving the department. The detector was facing the sternum or the urinary bladder, at a distance of 1 meter from and right in front of the patient. The practice for exiting the department differed according to whether the patient was referred to PET/CT or to SPECT/CT. PET/CT patients were discharged after imaging. Results: The median administered activity was 122 MBq in 53 ⁶⁸Ga-DOTATOC PET/CTs, 198 MBq in 15 ¹⁸F-FDOPA PET/CTs and 176 MBq in 13 ¹⁸F-FDG PET/CTs. The corresponding median EDR-1m (in µSv/h) were 4.8, 9.5 and 8.8 respectively facing the sternum, and 5.1, 10.1 and 9.5 respectively facing the bladder. SPECT/CT patients left the department earlier, just after radiopharmaceutical injection. The median administered activity was 170 MBq in 12 ¹¹¹In-pentetreotide SPECT/CTs and 186 MBq in 10 ¹²³I-mIBG SPECT/CTs. The corresponding median EDR-1m (in µSv/h) were 9.4, and 4.9 respectively at the level of the sternum, and 9.3 and 4.7 respectively at the level of the bladder. The EDR-1m was <20 µSv/h in all patients. Thus when exiting the nuclear medicine department, the NET patients injected with ⁶⁸Ga-DOTATOC or ¹²³I mIBG emitted an average EDR-1m roughly half of that of patients injected with other radiopharmaceuticals. This is a complementary argument for replacing SPECT by PET somatostatin-receptor imaging. Conclusion: Our current practice of allowing patients to exit after PET/CT imaging or just after SPECT radiopharmaceutical injection appears to be safe from a radiation protection point of view. Restrictive advice is unnecessary for NET patients discharged from the department.