It would be extremely useful to be able to apply a lower-order engineering design approximation to estimate heating effectiveness when there are multiple intracellular clusters of differing numbers of NPs. If it can be reasonably assumed that a closely packed nanoparticle cluster operates analogously to a lumped aggregate, a first approximation in a substantially simpler geometric model space is to assume that a single aggregate particle with the same volume of magnetic material can be used to simulate a nanoparticle cluster in an equivalent thermal sense, at least. Such an ellipsoid with the equivalent volume of dextran coating was placed at the same location in the cell. For this equivalent magnetic NP ellipsoid, the X- and Y-semi-axes are 98 nm and the Z-semi-axis is 147 nm (aspect ratio 1.5). At the same volume generation power, 3 × 1015 (W m−3), the ellipsoid-center temperature reaches 59.5 °C, at steady state (in less than 0.2 s), 10 °C higher than the individual NPs in Fig. 10; however, the 43 °C contour outside of the ellipsoid compares very favorably with the individual NP result of Fig. 10. Incidentally, the ellipsoid-center heating pattern blooms only very slightly between 0.2 and 30 s, and not at all thereafter. So, while the center temperature will be over-estimated, the heating effectiveness at distance ought to be represented with acceptable accuracy. The heating distribution is still quite disappointing, however, due to the intense vertical thermal gradients.