A radioconjugate composed of an affinity-matured antibody fragment, the A11 minibody, directed against human prostate stem cell antigen (PSCA), and conjugated with the radioisotope iodine I 124, that can potentially be used as an imaging agent for positron emission tomography (PET)/computed tomography (CT). The minibody moiety of iodine I 124-labeled anti-PSCA A11 minibody selectively targets and binds to PSCA. The PSCA-expressing tumor cells can then be visualized using PET/CT. PSCA, a cell surface antigen expressed in normal human prostate and bladder, is overexpressed in a variety of cancers, including bladder, pancreatic, and prostate cancer. The A11 minibody is formed by the fusion of a single chain Fv fragment with the immunoglobulin G1 CH3 domain. Check foractive clinical trials using this agent.