Background: 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is increasingly used to monitor response to multimodality cancer treatment. Preoperative short-course radiotherapy (SCRT) has been shown to improve outcome in locally advanced rectal cancer (LARC). We evaluated the value of FDGPET in monitoring response to SCRT.
Patients and methods: 32 patients with LARC scheduled for SCRT underwent FDG-PET, magnetic resonance imaging and endorectal ultrasound both before and after SCRT. A comparison group of 16 patients, undergoing preoperative radiochemotherapy (RCT), received an extra FDG-PET 17 days after starting RCT (effective dose of 30.6 Gy). For response assessment, FDG uptake (maximum standardized uptake value, SUVmax), percent SUVmax difference, tumor regression grade (TRG), and UICC downstaging and downsizing were considered.
Results: SCRT resulted in a significant median SUVmax reduction of 39.3%. Median SUVmax reduction did differ between SCRT and the early scans after 17 days of RCT (39.3 vs. 50.8%). Downstaging after SCRT was observed in 16/32, downsizing in 7/32 patients. There was no correlation between SUVmax reduction and downstaging/ downsizing or TRG.
Conclusion: For the first time, we were able to demonstrate functional response after SCRT. In contrast to morphological imaging and histopathology, our results indicate that FDG-PET can monitor early effects of SCRT. Further followup is warranted to establish SUVmax reduction as a surrogate marker for the response of SCRT.
2008 S. Karger AG, Basel.