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

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 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. 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.

On the biological efficiency of I-123 and I-125 decay on the molecular level.

PURPOSE: To evaluate DNA damage of Auger emitters by numerical modelling at the molecular level. MATERIAL AND METHODS: Energy emission spectra of I-123 and I-125 were used as input data for a computer code that simulates the complete transport of electrons and photons from the physical stage up to the primary chemical stage at 10(-7) s. The simulation was performed in a complex environment of liquid water, DNA structures and scavengers. Electron and photon interactions with the DNA molecules were carefully managed. Simulations were carried out with both I-123 and I-125 bound to a pBR322 plasmid or free in its vicinity. RESULTS: The distributions of direct and indirect single strand breaks (SSB) and double strand breaks (DSB) as a function of the kinetic energy of the emitted Auger electrons show that damage is caused primarily by electrons with energies lower than 800 eV, while higher energy electrons are mainly involved in indirect effects. The yields per unit energy emitted strengthen this fact. When compared to experimental values, the calculated yields of linearization (LE) and relaxation (RE) events show good agreement as well as does the ratio LE/RE for each radionuclide and the ratio I-125/I-123 in the case of LE.

Molecular basic data calculation for radiation transport in chromatin.

Differential and integral electron impact ionisation cross sections were calculated using the binary-encounter-Bethe theoretical model for each core particle molecules: the four DNA bases, the backbone (sugar phosphate), and the 19 amino acids constituent of histone proteins. The binding energies and populations of molecular orbitals were computed using General Atomic Molecular Electronic Structure System. At present, there are neither experimental nor other theoretical results on amino acid electron impact ionisation cross sections. Regarding DNA bases and backbone, our results show good agreement with those published in journals.