Yttrium-90 and Rhenium-188 Radiopharmaceuticals for Radionuclide Therapy

are available. Therapeutic radiopharmaceuticals, based on radionuclides decaying
by the emission of β particles, are preferred in most of these applications.
The radioisotopes 186 Re and 188 Re have favourable properties for therapy
[10.4]. They decay through the emission of high energy β particles and the
emission of γ photons ( 186 Re: T 1/2 = 90 h, E β = 1.1 MeV, E γ = 137 keV (~10%);
188 Re: T 1/2 = 16.7 h, E β = 2.1 MeV, E γ = 155 keV (~15%)), which allows evaluation
of the in vivo biodistribution of Re radiopharmaceuticals using a gamma camera.
While 186 Re is a reactor produced radioisotope, 188 Re can be obtained from a
188 W/ 188 Re radionuclide generator system. The chemistry of rhenium resembles
that of technetium. Rhenium-188 is a very attractive radioisotope for systematic
radiotherapy, with some key advantages, especially because it can be obtained
from a transportable 188 W/ 188 Re generator.
Currently, the radioisotope 90 Y is widely used for therapy. It can be obtained
from the decay of 90 Sr, which is, in turn, a high yield fission product. Yttrium-90
is a pure high energy β particle emitter, with E βmax = 2.2 MeV and T 1/2 = 64.1 h.
Furthermore, the path length of its β particles (r 95 = 5.9 mm) in tissues is a major
advantage in the treatment of solid tumours. In fact, higher particle energies and
longer penetration ranges in tissues could be of crucial help in the treatment of
large tumours.
10.2. RHENIUM-188 LABELLED BONE SEEKING AND
TUMOUR SPECIFIC AGENTS FOR RADIONUCLIDE THERAPY
10.2.1. Preparation of 186 Re HEDP
10.2.1.1. Materials and methods
Rhenium-186 was prepared by irradiation of 1–4 mg of metallic
rhenium target (3.6 mg of natural rhenium irradiated for 1 d at a neutron flux
of 5 × 10 13 neutrons·cm –2·s–1 ) in the nuclear reactor at the National Centre for
Scientific Research ‘Demokritos’ (Greece). The irradiated target, with an activity
of 62 mCi, was dissolved in 0.5–2 mL of hydrogen peroxide acid for 2 h and
subsequently evaporated to dryness. The residue was dissolved in water for
injection. The RCP of 186 ReO – 4 (ITLC SG methylethylketone) was >99%.
A solution of 186 –
ReO 4 (2.2 mL containing 0.5–2 mCi of 186 Re in
0.052–0.150 mg of metallic rhenium) was then transferred to a vial containing
HEDP. Three different samples of 186 Re HEDP, labelled as A, B and C, were
prepared with 52, 113 and 150 μg of metallic rhenium, respectively. For this
purpose, the standard kit prepared at Demokritos was modified, wherein the
pH of HEDP solutions was adjusted to 2.0–2.5 (labelling was performed at
170