[1] Univ Med Ctr, Tucson, AZ USA
[2] Univ Texas MD Anderson Canc Ctr, Houston, TX 77030 USA
[3] Univ Penn, Philadelphia, PA 19104 USA
[4] Chinese Acad Med Sci, Canc Hosp & Inst, Beijing, Peoples R China
[5] Univ Texas MD Anderson Canc Ctr, Dept Radiat Oncol, Houston, TX 77030 USA
[6] Univ Arizona, Dept Radiat Oncol, Tucson, AZ 85721 USA