Objective: In patients with soft tissue sarcoma (STS) the histological response (tumour grade regression: TGR) to neoadjuvant chemoradiotherapy (CRT) may influence the outcome. The main aim of the study was to evaluate the predictive value of 11C-methionine (MET) and 18F-FDG PET/CT in patients with STS treated with neoadjuvant CRT, correlating TGR with SUVmax (standardized uptake value) percentage variation before and after CRT.
Patients and methods: Nine patients with STS already scheduled for a neoadjuvant CRT and surgery were enrolled. They underwent MET and FDG PET/CT in a one-day procedure before and after the CRT. Pre-therapy SUVmax and the percentage variation of SUVmax for MET and FDG were correlated with TGR according to the Huvos grade. Grades I-II were considered as partial responders (PR) and grades III-IV as complete responders (CR).
Results: FDG pre-treatment mean SUVmax in PR patients was 7.1, while in CR patients it was 13.2. Pre-treatment mean MET SUVmax in PR patients was 75, while in CR patients it was 4.9. The mean percentage variation in FDG SUVmax, was -21.2% in PR patients and -745% in CR patients while that for MET SUVmax was 48% in PR patients and -53.9% in CR patients.
Conclusion: According to this preliminary study, the percentage variation in FDG before and after CRT seems to discriminate between PR and CR better than MET.