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. Methods: 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. Results: 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 mSv/h, respectively, facing the sternum, and 5.1, 10.1, and 9.5 mSv/h, respectively, facing the bladder. The meDian administered activity was 170 MBq in 12 111In-pentetreotide SPECT/CT stuDies and 186 MBq in 10 123IMIBG SPECT/CT stuDies. The corresponDing meDian EDR-1m was 9.4, and 4.9 mSv/h, respectively, at the level of the sternum, and 9.3 and 4.7 mSv/h, respectively, at the level of the bladder. The EDR-1m was less than 20 mSv/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. 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 being Discharged from the department.