Equivalent Dose Rate 1 Meter from Neuroendocrine Tumor Patients Exiting the Nuclear Medicine Department After Undergoing Imaging

Abstract

¹²³I-metaiodobenzylguanidine (MIBG) and ¹¹¹In-pentetrotide SPECT have been used for functional imaging of neuroendocrine tumors (NETs) for the last 2 decades. More recently, PET/CT imaging with ¹⁸F-FDG, ¹⁸F-fluorodihydroxyphenylalanine (FDOPA), and ⁶⁸Ga somatostatin-receptor ligands in NETs has been expanding. A literature search could find no direct measurements of the dose rate from NET patients exiting the nuclear medicine department after undergoing PET/CT with ¹⁸F-FDOPA or ⁶⁸Ga-DOTATOC, a somatostatin analog. <b>Methods:</b> We measured the dose rates from 93 NET patients on leaving the department after undergoing PET/CT or SPECT/CT in our centers. In total, 103 paired measurements of equivalent dose rate at 1 m (EDR-1m) from the sternum and urinary bladder were obtained. The detector faced the sternum or bladder and was 1 m away from and directly in front of the patient. The practice for exiting the department differed according to whether the patient had been referred for PET/CT or for SPECT/CT. PET/CT patients were discharged after imaging, whereas SPECT/CT patients left the department earlier, just after radiopharmaceutical injection. <b>Results:</b> The median administered activity was 122 MBq in 53 ⁶⁸Ga-DOTATOC PET/CT studies, 198 MBq in 15 ¹⁸F-FDOPA PET/CT studies, and 176 MBq in 13 ¹⁸F-FDG PET/CT studies. The corresponding median EDR-1m was 4.8, 9.5, and 8.8 μSv/h, respectively, facing the sternum, and 5.1, 10.1, and 9.5 μSv/h, respectively, facing the bladder. The median administered activity was 170 MBq in 12 ¹¹¹In-pentetreotide SPECT/CT studies and 186 MBq in 10 ¹²³I-MIBG SPECT/CT studies. The corresponding median EDR-1m was 9.4, and 4.9 μSv/h, respectively, at the level of the sternum, and 9.3 and 4.7 μSv/h, respectively, at the level of the bladder. The EDR-1m was less than 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 that of patients injected with other radiopharmaceuticals. This finding is a complementary argument for replacing SPECT by PET somatostatin-receptor imaging. <b>Conclusion:</b> 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 being discharged from the department.