TAC1 and neoplasm: Surprisingly, 68Ga-DOTA-substance P had comparable tumor to brain ratio as 68Ga-RGD peptides and 18F-FLT; however, the SUVs were very low in both tumor and brain regions in the case of 68Ga-substance P. Among 68Ga-RGD peptides and 18F-FLT, all the tumor to brain ratios were very similar not preferencing any of the studied tracers.