Hypoxia-imaging with 18F-Misonidazole and PET: Changes of kinetics during radiotherapy of head-and-neck cancer

Abstract Background and purpose PET with 18 F-Misonidazole (FMISO-PET) is a non-invasive method for measuring tumor hypoxia. We analysed changes of FMISO-uptake during radiotherapy and their impact on patient outcome. Materials and methods Fourteen patients with HNC underwent repeated FMISO-PET prior to radiotherapy and after 30Gy. Dynamic and static PET-scans (2+4h p.i.) were acquired. FMISO-uptake was quantified by calculating standard uptake values (SUV) and tumor-muscle-ratios (TMR). Kinetic curve types representing tissue hypoxia were defined. Change of curve type was correlated with patient outcome. Results The mean SUV 4h p.i. and the TMR decreased significantly during radiotherapy. SUV decreased clearly in 12/14 patients, and increased in 2 patients. TMR decreased in 11 patients, and increased in 3 patients. Prior to radiotherapy, three different shapes of kinetic curve types indicative for the degree of hypoxia could be defined in 12/14 patients: (1) accumulation type (severe hypoxia ( n =8)), (2) intermediate type (intermediate degree of hypoxia ( n =3)), and (3) wash-out type (low degree of hypoxia ( n =1)). Curve type changed towards a lower degree of hypoxia at 30Gy in all but 3 patients. In three patients curve type remained unchanged. Conclusions The changes in tumor FMISO-uptake during radiotherapy indicate radio-induced reoxygenation.