This book describes in detail a clinical project that reveals the tumoricidal efficacy of Auger and internal conversion electrons, emitted from n.c.a. 111In and implemented in oncology as a treating armamentarium for peptide receptor radionuclide therapy (PRRT), targeting small size (    20 mm) tumors and micro-metastases.The keen interest in n.c.a. 111In began when it was observed that its Auger electron emission could be highly radiotoxic, due to its high LET when it decayed in the vicinity of cellular DNA. The somatostatin analog octreotide, labeled with [111In-diethylenetriaminepentaacetic acid (DTPA0-D-Phe1)] is an established diagnostic agent for the imaging of somatostatin receptor-positive neuro- (or non-neuro) endocrine tumors.