In this study, we compared DOTA-conjugated trastuzumab IgG,F(ab')2 or Fab complexed to 111In or 225Ac for SPECT/CT imaging and α-particle RIT of subcutaneous(s.c.)HER2-positive 164/8-1B/H2N.luc+ human BC tumorsin NRG mice. The gene discussed is ERBB2; the disease is breast cancer.