HSV-tk: herpes simplex virus thymidine kinase; SBRT: stereotactic body radiation therapy; CMV: cytomegalovirus; GBM: glioblastoma multiforme; GCV: ganciclovir; XRT:- radiotherapy; Adv-tk: adenovirus-mediated herpes simplex virus thymidine kinase; 5-FC: 5-fluorocytosine; TOCA511: retroviral replicating vector that selectively infects cancer cells and delivers cytosine deaminase. The gene discussed is TKT; the disease is cancer.