Hector,

%ID depends greatly on the targeting construct that is being used. Complete antibodies (150 kDa) target slowly and don't typically penetrate tumors well. Typical %ID for antibodies is

Thanks for your answer professor Speer. I have been reviewing the literature on this and indeed I have noticed such small %ID tumor uptake for radiolabeled antibodies and peptides (although most researchers still report SUV values). This explains why such huge amounts of radioactivity (up to 200 mCi of 177Lu or 90Y per cycle) and in up to 3 - 6 cycles are required for some tumor control. I work with small animals and we usually quantify max tumor uptake of antibodies of ~10-15 %ID/g, which corresponds to ~2 - 3 %ID uptake for a 200mg tumor implanted in a 20 g mouse. The 100 to 1000-fold increase in %ID explains why so many publications report tumor regression in small animals after injection of only a few mCi. I have been thinking about this in order to determine the feasibility of using the theranostic nuclide 64Cu for targeted therapy in humans and not just in mice. As you pointed it out, better targeting vectors are necessary that offer higher targeting efficiencies in terms of %ID of %ID/g.