64 Cu-/ 177 Lu-Cetuximab Theranostic Pair: May the Single 64 Cu-Cetuximab Diagnostic Scan Be Acquired at Any Time After Injection?

Two independent equations were recently proposed for estimating 177 Lu-cetuximab cumulative activity, in a preclinical situation, from an initial 64 Cu-cetuximab diagnostic scan acquired at peak time of decay-uncorrected ( t peak-uncorr ) or decay-corrected ( t peak-corr ) time-activity curve of trapped 64 Cu-cetuximab, respectively. The standard uptake ratio (SUR) measured at t peak-uncorr or t peak-corr turned out to be a key metric in each equation, respectively. However, acquiring the diagnostic scan at t peak-uncorr or t peak-corr might be a limitation of the proposed method. Therefore, in an attempt to overcome this limitation, this note aims at theoretically investigating whether SUR( t peak-uncorr ) and/or SUR( t peak-corr ) could be derived from a diagnostic scan acquired at any time postinjection.