Size of microspheres for treatment of hepatic malignancies

1.2.2.1 Size of microspheres for treatment of hepatic malignancies

The size of the microsphere is an important factor for the distribution in the liver and
tumour. The production parameters of microspheres can be modified to result in high
yields of spheres with the desired diameter. For example, lowering the stirring rate
during production and a higher viscosity of the aqueous phase, result in increasing
diameters of the polymeric microspheres. Although the size of the microspheres can

be regulated by production methods, a sifting step is necessary after production of
cold or radioactive spheres.
A range of sizes has been reported in the literature with microsphere diameters
varying from 13 to 75 μm [14,22,23,35,36]. The widely used 90Y glass microspheres
have a mean diameter of 22 μm with a range of 15 to 30 μm [10,12,37].
Larger microspheres, 40-50 μm, are distributed more homogeneously in the liver
and with fewer spills to other organs such as lungs and spleen than smaller particles.
However, with larger particles the tumour/liver ratio decreases. Microspheres of
around 30 μm are the optimum size for hepatic radionuclide therapy, as they are most
evenly distributed within the normal liver tissue, yet still provide a concentrated dose
of radiation to tumour tissue [8,38,39]. Distribution of intra-arterial microspheres with
a diameter of 32 μm was extensively investigated in the microvasculature of tumour
in human liver by Campbell et al. [40]. Microspheres were found to deposit
preferentially in the richly vascularized periphery of the tumour.