Hypofractionated RT: It is generally accepted that the presence of chronically hypoxic cells within tumors may be an important cause of radioresistance and resultant local failure in radiotherapy, particularly in large solid tumors such as locoregionally advanced NSCLC. In-vitro experiments indicated that the dose needed to kill severely hypoxic cells is on the order of 2 or 3 times the dose needed for oxic cells. Therefore, delivering a higher RT dose to the tumor may result in higher tumor cell kill and improved local control. One of the approaches to increase RT dose is to use hypofractionated RT, which not only increases the dose, but also reduces the overall treatment time. The radiobiological rationale for hypofractionated RT was described by Mehta et al (Mehta et al, 2001). Based on these theoretical assumptions, University of Wisconsin has recently completed a dose escalation study of progressively increasing fraction sizes in thoracic RT for lung cancer. Such larger RT fraction sizes may require "tighter" radiation fields (to achieve reliable normal-tissue sparing) and improved precision of RT delivery, something that is afforded by the SBF (Stereotactic Body Frame) immobilization and daily CT scan based image verification of tumor position. More experiences have been reported in the literature on hypofractionated regimens for lung cancer. Japanese investigators (Nagata Y et al, 2002) treated 40 patients with T1-T3N0 tumors or lung metastases with 10-12 Gy per fraction to a total of 40-48 Gy. No pulmonary (or other) complications >Grade 2 were observed and the local control was 100% in the subgroup of primary lung tumors. Another group from Japan (Onimaru R et al, 2003) reported on 45 patients with primary lung tumors up to 6cm receiving 7.5 Gy per fraction to 60 Gy (lesions <3cm) or 6 Gy per fractions to 48 Gy (lesions 3-6cm). One patient with a central tumor died of a radiation-induced ulcer in the esophagus. One patient with a peripheral lesion experienced Grade 2 chest wall pain. The 3-year local control rate was 80%. No adverse respiratory events were noted.