Internal radiation dose assessment of radiopharmaceuticals prepared with cyclotron‐produced ^99mTc

Abstract

Purpose Technetium‐99m (99mTc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99Mo/99mTc generators as the β−decay product of the 99Mo (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 [100Mo(p,2n)99mTc], have the potential to be both reliable and relatively cost‐effective. However, results showed that the 99mTc extracted from proton‐bombarded 100Mo‐enriched targets contains small quantities of several Tc radioisotopes (93mTc, 93Tc, 94Tc, 94mTc, 95Tc, 95mTc, 96Tc, and 97mTc). 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 99mTc (CP‐99mTc) using 99.05% 100Mo‐enriched metallic targets. Methods Four 99mTc 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 99mTc. 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. 94mTc and 93mTc 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 96Tc, followed by 95Tc and 94Tc. 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 94mTc and 93mTc 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 94Tc and 95Tc radioisotopes in the CP‐99mTc solution exceed the limits established by the European Pharmacopoeia, CP‐99mTc radiopharmaceuticals could be used in routine nuclear medicine diagno...

Influence of enriched 100Mo on Mo reaction yields

“…In their studies [15] and [20], Hou et al reported that at proton beam energies below 20 MeV, the contents of [94][95][96][97] Mo contribute more than the content of 98 Mo to the dose increase and image quality degradation. Recent studies by [24,25] figure 10.…”

“…The 98 Mo DCC should also be considered if the proton beam energies are greater than 20 MeV, which is the threshold for the 98 Mo(p,3n) 96 Tc and 98 Mo(p,3n) 96m Tc reactions [14,36]. 96m Tc deexcites to 96 Tc with 98% probability [37], and 96 Tc is reported to be one of the major impurities affecting the radiation dose and image quality [15,20,24,25]. Therefore, the 99.815% and 99.86% enriched 100 Mo products, whose 98 Mo DCCs as well Table 3.…”

“…• Production of 99m Tc via the 100 Mo(p,2n) 99m Tc reaction using medical cyclotrons [14][15][16][17][18][19][20][21][22][23][24][25].…”

“…are used in accelerator production of 99 Mo [2,6,9,11], and the former of which is used in cyclotron production of 99m Tc [2,16,18,21,[23][24][25]27]. We hereafter refer to Mo metal as Mo met to distinguish it from the Mo element.…”

Molybdenum-99 production pathways and the sorbents for 99Mo/99mTc generator systems using (n, γ) 99Mo: a review

“…Although, all the accelerator-based strategies are under development as major alternatives but the issues related to the practical limits of irradiation volumes and low crosssections of the reaction routes need careful assessment [3]. For example, the direct 99m Tc production from protonbombarded 100 Mo-enriched targets using cyclotron is considered as reliable and cost-effective alternative production routes [32]. Qaim et al [33] reported that the ratio of atoms of long-lived 99g Tc and 98 Tc to those of 99m Tc is appreciably higher in cyclotron production than in generator production of 99m Tc.…”