Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 51 (2018)

Wet chemistry processes utilized in development of211
Rn/211 At generator for targeted alpha therapy
Y. Shin,∗1 K. Kawasaki,∗2 N. Yamada,∗1A. Yokoyama,∗2 I. Nishinaka,∗4 S. Yanou,∗5 and H. Haba∗5

The short path length and high linear energy transfer of alpha particles are expected to facilitate targetedalpha therapy in tumor treatment. One of the promising nuclides among the various alpha emitters is 211 At,
which has a half-life of 7.21 h. This nuclide attracts
much attention because of its suitable half life and theexpected chemical properties of the element, and thishas motivated a large number of preclinical studies onAt chemistry.1–3) As regards improvement of the 211 At
availability, development of a 14.6-h 211 Rn generator,
where 211 Rn is a parent nuclide of 211 At, can potentially provide nuclides in a wider range of locations distant from the accelerator facilities in which they areproduced. However, At chemistry has not been wellstudied in relation to Rn decay and further knowledgeis needed to control its behaviors in the required successive chemical processes.4) The aim of this study was
to investigate the wet chemistry processes of At so as
to realize a 211 Rn/211 At generator that may facilitatea prevalent technology.
Radon-211 was produced through irradiation of a
stack of Bi targets with 60-MeV 7 Li3+ beams from theJapan Atomic Energy Agency (JAEA) tandem accelerator via the 209 Bi(7 Li, 5n) 211 Rn nuclear reaction.
After the irradiation, the Bi target was dissolved innitric acid solution and diluted with distilled water.
Then, the produced 211 Rn was transferred to an organic phase, i.e., dodecane, through solvent extraction.
The trapped 211 Rn was then allowed to stand for overhalf a day to generate 211 At. Back-extraction of 211 At
was performed using alcohol with an oxidizing agent.
In this study, to obtain the 211 At distribution ratios between the dodecane and ethanol (EtOH) solution with an oxidizing agent, the Bi target, which wasirradiated at the RIKEN Azimuthally Variable Field(AVF) cyclotron, was delivered to Kanazawa University, dissolved in nitric acid, and diluted to a 1 M
solution in acid concentration. The dodecane solution, into which At species were extracted from thenitric acid solution, was subjected to extraction experiments with and without an oxidization agent, i.e.,
∗1
∗2
∗3
∗4

∗5Institute and College of Science and Engineering, Kanazawa
UniversityGraduate School of Natural Science and Technology,
Kanazawa University
Fukushima Global Medical Science Center, Fukushima Medical Unversity
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology
RIKEN Nishina Center- 228 -100.010.0

DK. Washiyama,∗31.00.1㻜㻞㻜㻠㻜㻢㻜㻤㻜㻝㻜㻜

EtOH (volume %)Fig. 1. Distribution values of 131 I (open symbols) and 211 At(closed symbols) for extraction with (circles) and without (triangles) an oxidizing agent.

N -Bromosuccinimide. The results were compared withthose of the same experiments performed with a commercially available I-131 isotope.
After the back extraction to the EtOH solution, eachphase was subjected to measurements with a liquid
scintillation counter, to determine the back extraction
distribution, D, of 211 At. Hence, we found that only
At exhibit a notable eﬀect of oxidation, as shown in
Fig. 1. Here, the distributions were obtained from theratios of the radioactivity in the EtOH solution to thatin the dodecane. We also aimed to control the extraction behavior of the At from the nitric acid solution
by using an ionic liquid with a crown ether. For thecombination of 1-butyl-3-methylimidazolium Bis (triﬂuoromethanesulfonyl) imide and 18-crown-6, the extraction system was found to be promising because anextraction rate of up to 90% was attained at low acidconcentrations.
References1) F. Guérard, J-F. Gestin, M. W. Brechbiel, Cancer Biother. Radiopharm. 28, 1 (2013).
2) D. S. Wilbur, Nat. Chem. 5, 246 (2013).
3) M. R. Zalutsky, M. Pruszyński, Curr. Radiopharm. 4,177 (2011).
4) E. Maeda, A. Yokoyama, T. Taniguchi, K. Washiyama,
I. Nishinaka, J. Radioanal, Nucl. Chem. 303(2), 1465
(2015).