Statistics of Comparative in vitro and in vivo cytotoxic activity of (E)-5-(2-bromovinyl)-2’-deoxyuridine (BVDU) and its arabinosyl derivative,(E)-5-(2-bromovinyl)-1-b-D-arabinofuranosyluracil (BVaraU), against tumor cells expressing either the Varicella zoster or the Herpes simplex virus thymidine kinase