III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Accelerator production and chemical separation of theranostic
radionuclide 141 Ce
K. Ooe,∗1,∗2 T. Watabe,∗1,∗2 Y. Shirakami,∗2 A. Nambu,∗3 H. Haba,∗3 and J. Hatazawa∗4

∗1
∗2
∗3
∗4

get, high radioactivities of short-lived 38 K (T1/2 =7.636 min) and 34m Cl (T1/2 = 31.99 min) were observed. These by-products are considered to be produced from nat Cl in the BaCl2 target and α beam.
Because of these by-products, the radiation dose fromthe irradiated BaCl2 target was quite high, and theγ-ray of 141 Ce was only observed after the decay ofthese by-products. On the other hand, in the γ-ray
spectrum of 141 Ce produced with BaO, no such interference nuclides were observed, and the γ-ray of 141 Ce
was observed soon after the end of irradiation. Therefore, BaO is considered to be a suitable target material
for the production of 141 Ce by the α beam.
The elution curves for nat Ba and 141 Ce from the Ln
resin are shown in Fig. 1 (BaO was used as the targetmaterial). nat Ba was eluted before 141 Ce with 0.01 M
HCl. After the elution of nat Ba, 141 Ce was recoveredby elution with 1 M HCl. The recovery yield for 141 Ce
was greater than 99%. The contamination of nat Ba
into 141 Ce fraction was calculated as less than 3 μgin the ICP-MS measurement: the separation factor of141
Ce for nat Ba is greater than 104 .
In the next study, the radiopharmaceutical labelingof 141 Ce will be investigated.

0.01 M HCl

Eluted amount of100
natBa or 141Ce (%)

Because all of the therapeutic radionuclides usedin clinical practice in Japan are imported from othercountries, domestic production using accelerators is desirable for the stable supply of therapeutic nuclides.
Cerium-141 (141 Ce, T1/2 = 32.5 d) is a candidate
radionuclide for theranostics (therapeutics + diagnosis) and can be produced in the 138 Ba(α, n)141 Ce reaction using accelerators. This nuclide emits β-particles(maximum β energy: 580.7 keV), which can be applied
to the therapy of tumors, as well as a γ-ray with an energy of 145.4 keV (branching ratio: 48.2%), which canbe used for imaging by single photon emission computed tomography (SPECT). In particular, 141 Ce isexpected to be useful for SPECT imaging because theenergy of the γ-ray of 141 Ce is similar to that of 99m Tc(140 keV), which is the most widely used SPECT nuclide in clinical application. However, 141 Ce has beenrarely applied to nuclear medicine. In this study, asuitable target material of nat Ba for the accelerator
production of 141 Ce was investigated. A chemical separation method for 141 Ce from the irradiated nat Ba target was also investigated through column chromatography with a Ln resin (extraction chromatographic resinwith di(2-ethylhexyl) phosphoric acid).
For the determination of a suitable target materialof nat Ba, BaCl2 and BaO pellets (both approximately
100 mg) were irradiated with a 29-MeV alpha beam
(beam intensity: 1.3 particle μA, irradiation time:10 min) using the RIKEN K70 AVF cyclotron. The
irradiated nat Ba targets were subjected to γ-ray spectrometry with a Ge semiconductor detector. In thechemical separation of 141 Ce from the nat Ba target,
the irradiated nat Ba target (approximately 100 mg)
was dissolved in 3 mL of 1 M HCl. After evaporation to dryness, the residue was dissolved in 3 mL of0.01 M HCl solution and then fed into a Ln resin column (5-mm diameter × 50-mm height). nat Ba waseluted by 0.01 M HCl, following which 141 Ce was elutedby 1 M HCl solution by referring to the literature.1)
Each eluted sample (1 mL) was subjected to γ-ray
spectrometry with the Ge detector for the determination of 141 Ce radioactivity. After measurement withthe Ge detector, the concentration of nat Ba in each
eluted sample was measured by inductively coupledplasma mass spectrometry (ICP-MS).
In the production of 141 Ce from the BaCl2 tar-

1 M HCl

141Ce (Ȗ-ray spectrometry)80

natBa (ICP-MS)

60
40
200024 6 8 10 12 14 16 18
Elution volume (mL)

Fig. 1. Elution curves of nat Ba and 141 Ce in chromatographic separation with Ln resin.

Reference1) E. P. Horwitz, C. A. A. Bloomquist, J. Inorg. Nucl.
Chem. 37, 425 (1975).

Department of Nuclear Medicine and Tracer Kinetics, Graduate School of Medicine, Osaka University
Institute for Radiation Sciences, Osaka University
RIKEN Nishina Center
Research Center for Nuclear Physics, Osaka University- 130 -1