Resins

Resins

Resin-based microspheres are much favoured for radio-embolization. Chloride salts of
holmium and yttrium were added to cation exchange resins. Different resins were
investigated by Schubiger et al. [19], amongst which were Bio-Rex 70, Cellex-P,
Chelex 100, Sephadex SP and AG 50W-X8. The resins with 90Y bound to the
carboxylic acid exchange groups of the acrylic polymer were sterilised and used for
renal embolization of pigs. Only the pre-treated Bio-Rex 70 resulted in applicable
particles, with a retention of beta activity in the target organ of >95% of injected dose,
and no histologically detectable particles in lung tissue samples [20].
As well as Bio-Rex 70, Aminex resins (Bio-Rad Inc. Hercules CA, USA) loaded
with 166Ho or 188Re, also resulted in applicable preparations. Turner et al. [14]
prepared microspheres by addition of 166Ho-chloride to the cation exchange resin
Aminex A-5, which has sulphonic acid functional groups attached to styrene
divinylbenzene copolymer lattices. Reproducible, non-uniform distributions of the

166Ho-microspheres throughout the liver were observed on scintigraphic images,
following intrahepatic arterial administration in pigs. This predictable distribution
allowed these investigators to determine the radiation absorbed dose from a tracer
activity of 166Ho-microspheres, and to define the administered activity required to
provide a therapeutic dose.
Aminex A-27 was labelled with 188Re by adding 188Re-perrhenate and SnCl2 to
vacuum-dried resin particles [21]. The mixture was boiled and centrifuged and
microspheres were separated and resuspended in saline. Spheres were tested by direct
intratumoural injection into rats with hepatoma. Survival over 60 days was
significantly better in the treated vs. the control group (80% vs. 27%).
Investigators from Australia and Hong Kong have used unspecified resin-based
particles labeled with 90Y for treatment of patients with primary or secondary liver
cancer [22,23]. The spheres had a diameter of 29-35 μm, a density of 1.6 g/ml and a
specific activity of approximately 30-50 Bq per sphere. Treatment was well tolerated
with no bone-marrow or pulmonary toxicity. The median survival was 9.4 months
(range 1.8-46.4) in 71 patients, and the objective response rate in terms of drop in
tumour marker levels was higher than that based on reduction in tumour volume
shown by computed tomography [15,24].