Pretreatment 18F-FAZA PET Predicts Success of Hypoxia-Directed Radiochemotherapy Using

We evaluated the predictive value of PET using the hypoxia tracer 18F-fluoroazomycin arabinoside (18F-FAZA) for success of radiotherapy in combination with tirapazamine, a specific cy-totoxin for hypoxic cells. Methods: Imaging was performed on EMT6 tumor-bearing nude mice before allocating mice into 4 groups: radiochemotherapy (RCT: 8 fractions of 4.5 Gy within 4 d combined with tirapazamine, 14 mg/kg), radiotherapy alone (RT), chemotherapy alone (tirapazamine) (CHT), or control. Treat-ment success was assessed by several tumor growth assays, including tumor growth time from 70 to 500 mL and absolute growth delay (aGD). The median pretreatment 18F-FAZA tumor-to-background ratio served as a discriminator between ‘‘hypoxic’’ and ‘‘normoxic’ ’ tumors. Results: The mean tumor growth was significantly accelerated in hypoxic control tumors (growth time from70 to 500mL, 11.0 d) comparedwith normoxic control tumor