Assessment of response to neoadjuvant radiochemotherapy with F-18 FLT and F-18 FDG PET/CT in patients with rectal cancer.

OBJECTIVE The comparison of 2-deoxy-2-[18F]fluoro-D-glucose (F-18 FDG) and 3'-deoxy-3'-[18F]fluorothymidine (F-18 FLT) imaging in patients with rectal cancer before and after neoadjuvant radiochemotherapy (RCT) in relation to histopathology and immunohistochemistry obtained from surgery. METHODS 20 consecutive patients (15 m, 5 f), mean age of 65 ± 10 years were included into this prospective study with a mean follow-up of 4.1 ± 0.8 years. RESULTS Among histopathological responders (n = 8 out of 20), posttreatment F-18 FLT and F-18 FDG scans were negative in 75 % (n = 6) and 38 % (n = 3), respectively. The mean response index (RI) was 61.0 % ± 14.0 % for F-18 FLT and 58.7 % ± 14.6 % for F-18 FDG imaging. Peritumoral lymphocytic infiltration (CD3 positive cells) was significantly related to posttreatment SUVmax in F-18 FDG but not F-18 FLT studies. CONCLUSION A significant decrease of SUVmax in F-18 FDG and F-18 FLT studies could be seen after RCT. Negative posttreatment F-18 FLT studies identified more histopathological responders.