Laura Meléndez-Alafort1, Guillermina Ferro-Flores2, Laura De Nardo3, Michele Bello3, Marta Paiusco4, Anna Negri4, Alessandra Zorz4, Nikolay Uzunov5, Juan Esposito6, Antonio Rosato1,7. 1. Veneto Institute of Oncology IOV-IRCCS, Via Gattamelata 64, Padova, 35138, Italy. 2. Laboratorio Nacional de Investigación y Desarrollo de Radiofármacos-CONACyT, Instituto Nacional de Investigaciones Nucleares, Carretera México-Toluca S/N. La Marquesa, Ocoyoacac, Estado de México, 52750, México. 3. Department of Physics and Astronomy, University of Padova, Via Marzolo 8, Padova, 35131, Italy. 4. Medical Physics Department, Veneto Institute of Oncology IOV-IRCCS, Via Gattamelata 64, Padova, 35138, Italy. 5. Faculty of Natural Sciences, University of Shumen, 115 Universitetska str., Shumen, 9712, Bulgaria. 6. Legnaro National laboratories, National Institute of Nuclear Physics, Viale della Università 2, Legnaro, 35020, Italy. 7. Department of Surgery, Oncology and Gastroenterology, University of Padova, Via Gattamelata 64, Padova, 35138, Italy.
Abstract
PURPOSE: Technetium-99m (99m Tc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99 Mo/99m Tc generators as the β- decay product of the 99 Mo (T½ = 66 h) parent nuclide. This latter is obtained as a fission product in nuclear reactors by neutron-induced reactions on highly enriched uranium. Alternative production routes, such as direct reactions using proton beams on specific target materials [100 Mo(p,2n)99m Tc], have the potential to be both reliable and relatively cost-effective. However, results showed that the 99m Tc extracted from proton-bombarded 100 Mo-enriched targets contains small quantities of several Tc radioisotopes (93m Tc, 93 Tc, 94 Tc, 94m Tc, 95 Tc, 95m Tc, 96 Tc, and 97m Tc). The aim of this work was to estimate the dose increase (DI) due to the contribution of Tc radioisotopes generated as impurities, after the intravenous injection of four radiopharmaceuticals prepared with cyclotron-produced 99m Tc (CP-99m Tc) using 99.05% 100 Mo-enriched metallic targets. METHODS: Four 99m Tc radiopharmaceuticals (pertechnetate, sestamibi (MIBI), hexamethylpropylene-amine oxime (HMPAO) and disodium etidronate (HEDP)) were considered in this study. The biokinetic models reported by the International Commission on Radiological Protection (ICRP) for each radiopharmaceutical were used to define the main source organs and to calculate the number of disintegrations per MBq that occurred in each source organ (Nsource ) for each Tc radioisotope present in the CP-99m Tc solution. Then, target organ equivalent doses and effective dose were calculated for each Tc radioisotope with the OLINDA/EXM software versions 1.1 and 2.0, using the calculated Nsource values and the adult male phantom as program inputs. Total effective dose produced by all Tc isotopes impurities present in the CP-99m Tc solution was calculated using the fraction of total activity corresponding to each radioisotope and compared with the effective dose delivered by the generator-produced 99m Tc. RESULTS: In all cases, the total effective DI of CP-99m Tc radiopharmaceuticals calculated with either versions of the OLINDA software was less than 10% from 6 up to 12 h after EOB. 94m Tc and 93m Tc are the Tc radioisotopes with the highest concentration in the CP-99m Tc solution at EOB. However, their contribution to DI 6 h after EOB is minimal, due to their short half-lives. The radioisotopes with the largest contribution to the effective DI are 96 Tc, followed by 95 Tc and 94 Tc. This is due to the types of their emissions and relatively long half-lives, although their concentration in the CP-99m Tc solution is five times lower than that of 94m Tc and 93m Tc at the EOB. CONCLUSIONS: The increase in the radiation dose caused by other Tc radioisotopes contained in CP-99m Tc produced as described here is quite low. Even though the concentrations of the 94 Tc and 95 Tc radioisotopes in the CP-99m Tc solution exceed the limits established by the European Pharmacopoeia, CP-99m Tc radiopharmaceuticals could be used in routine nuclear medicine diagnostic studies if administered from 6 to 12 h after the EOB, thus maintaining the effective DI within the 10% limit.
PURPOSE: Technetium-99m (99m Tc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99 Mo/99m Tc generators as the β- decay product of the 99 Mo (T½ = 66 h) parent nuclide. This latter is obtained as a fission product in nuclear reactors by neutron-induced reactions on highly enriched uranium. Alternative production routes, such as direct reactions using proton beams on specific target materials [100 Mo(p,2n)99m Tc], have the potential to be both reliable and relatively cost-effective. However, results showed that the 99m Tc extracted from proton-bombarded 100 Mo-enriched targets contains small quantities of several Tc radioisotopes (93m Tc, 93 Tc, 94 Tc, 94m Tc, 95 Tc, 95m Tc, 96 Tc, and 97m Tc). The aim of this work was to estimate the dose increase (DI) due to the contribution of Tc radioisotopes generated as impurities, after the intravenous injection of four radiopharmaceuticals prepared with cyclotron-produced 99m Tc (CP-99mTc) using 99.05% 100 Mo-enriched metallic targets. METHODS: Four 99m Tc radiopharmaceuticals (pertechnetate, sestamibi (MIBI), hexamethylpropylene-amine oxime (HMPAO) and disodium etidronate (HEDP)) were considered in this study. The biokinetic models reported by the International Commission on Radiological Protection (ICRP) for each radiopharmaceutical were used to define the main source organs and to calculate the number of disintegrations per MBq that occurred in each source organ (Nsource ) for each Tc radioisotope present in the CP-99mTc solution. Then, target organ equivalent doses and effective dose were calculated for each Tc radioisotope with the OLINDA/EXM software versions 1.1 and 2.0, using the calculated Nsource values and the adult male phantom as program inputs. Total effective dose produced by all Tc isotopes impurities present in the CP-99mTc solution was calculated using the fraction of total activity corresponding to each radioisotope and compared with the effective dose delivered by the generator-produced 99m Tc. RESULTS: In all cases, the total effective DI of CP-99mTc radiopharmaceuticals calculated with either versions of the OLINDA software was less than 10% from 6 up to 12 h after EOB. 94m Tc and 93m Tc are the Tc radioisotopes with the highest concentration in the CP-99mTc solution at EOB. However, their contribution to DI 6 h after EOB is minimal, due to their short half-lives. The radioisotopes with the largest contribution to the effective DI are 96 Tc, followed by 95 Tc and 94 Tc. This is due to the types of their emissions and relatively long half-lives, although their concentration in the CP-99mTc solution is five times lower than that of 94m Tc and 93m Tc at the EOB. CONCLUSIONS: The increase in the radiation dose caused by other Tc radioisotopes contained in CP-99mTc produced as described here is quite low. Even though the concentrations of the 94 Tc and 95 Tc radioisotopes in the CP-99mTc solution exceed the limits established by the European Pharmacopoeia, CP-99mTc radiopharmaceuticals could be used in routine nuclear medicine diagnostic studies if administered from 6 to 12 h after the EOB, thus maintaining the effective DI within the 10% limit.
Authors: Koen Van Laere; Michel Koole; Christopher Cawthorne; Paul Maguire; Joel Mercier; David Sciberras; Kim Serdons; Guy Bormans; Jan de Hoon Journal: EJNMMI Phys Date: 2021-04-23
Authors: Laura De Nardo; Gaia Pupillo; Liliana Mou; Juan Esposito; Antonio Rosato; Laura Meléndez-Alafort Journal: Med Phys Date: 2022-02-20 Impact factor: 4.506