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

Two independent equations were recently proposed for estimating Lu-177-cetuximab cumulative activity, in a preclinical situation, from an initial Cu-64-cetuximab diagnostic scan acquired at peak time of decay-uncorrected (t(peak-uncorr)) or decay-corrected (t(peak-corr)) time-activity curve of trapped Cu-64-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.