However, a recent review suggested that hypo-fractionated RT (HFRT) of ≥ 5 Gy in a single or a few fractions results in a different tumor radiobiology leading to increased endothelial cell apoptosis through the release of mitochondrial cytochrome C triggered by acid sphingomyelinase (ASMase) induced ceramide release or by de novo synthesis of ceramide [10]. The gene discussed is SMPD1; the disease is neoplasm.