11C-Methionine positron emission tomography as an early predictor of outcome in bone and soft tissue sarcomas treated by carbon ion radiotherapy

Abstract

3098 Background: The development of the novel carbon ion radiotherapy (CIRT) in the treatment of refractory cancers has resulted in the need for a way to accurately evaluate patients' prognosis. Amino acid metabolism of cancer is associated with numerous catabolic processes favoring tumor growth. As an essential amino acid, L-methionine plays a central role in the altered metabolism of cancer cells. We initially evaluated whether MET uptake and its change measured by PET after carbon ion radiotherapy were the early survival predicators in patients with bone and soft tissue sarcomas. Methods: MET PET was prospectively performed in 62 patients with bone and soft tissue sarcomas before and within one month after CIRT. Tumor MET uptake was measured with the semiquantitative tumor-to-nontumor ratio (T/N ratio). The MET uptake in the tumor and relevant clinical parameters were entered into univariate and multivariate survival analysis. Results: The overall median survival time was 20 months. Patients with a baseline T/N ratio of ≤ 6 had a significant better survival than patients with a baseline T/N ratio > 6 (2-year survival rate: 69.4% versus 32.3%, P=0.01). Patients with a post CIRT ratio of ≤ 4.4 had a better survival than that with a post CIRT ratio > 4.4 (2-year survival rate: 63.7% versus 41.3%, P=0.01). A significant higher survival rate was observed in patients with posttherapeutic MET uptake change of > 30% than patients in lower change group (2-year survival rate: 74.6% versus 41.6%, P=0.049). The multivariate analysis showed that both baseline and postCIRT T/N ratio were statistically significant independent predictors of patient survival. Tumors with larger T/N ratio had a significantly poorer prognosis. Conclusions: MET uptake, as measured by either baseline or postCIRT T/N ratio was an independent predictor of survival in patients with bone and soft tissue sarcomas treated by CIRT, while posttherapeutic MET uptake change might have potential value for the same purpose. No significant financial relationships to disclose.