Purpose: The aim of this study is to evaluate the toxicity of
holmium-166 poly(L-lactic acid) microspheres administered
into the hepatic artery in pigs.
Methods: Healthy pigs (20–30 kg) were injected into the
hepatic artery with holmium-165-loaded microspheres
(165HoMS; n=5) or with holmium-166-loaded microspheres
(166HoMS; n=13). The microspheres’ biodistribution
was assessed by single-photon emission computed
tomography and/or MRI. The animals were monitored
clinically, biochemically, and (166HoMS group only) hematologically
over a period of 1 month (165HoMS group) or
over 1 or 2 months (166HoMS group). Finally, a pathological
examination was undertaken.
Results: After microsphere administration, some animals
exhibited a slightly diminished level of consciousness and a
dip in appetite, both of which were transient. Four lethal
adverse events occurred in the 166HoMS group due either to
incorrect administration or comorbidity: inadvertent delivery
of microspheres into the gastric wall (n=2), preexisting
gastric ulceration (n=1), and endocarditis (n=1). AST levels
were transitorily elevated post-166HoMS administration. In
the other blood parameters, no abnormalities were observed.
Nuclear scans were acquired from all animals from the
166HoMS group, and MRI scans were performed if available.
In pigs fromthe 166HoMS group, atrophy of one or more liver
lobes was frequently observed. The actual radioactivity distribution
was assessed through ex vivo 166mHo measurements.
Conclusion: It can be concluded that the toxicity profile of
HoMS is low. In pigs, hepatic arterial embolization with
166HoMS in amounts corresponding with liver-absorbed
doses of over 100 Gy, if correctly administered, is not
associated with clinically relevant side effects. This result
offers a good perspective for upcoming patient trials
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