Purpose: The aim of this study was to investigate metabolic and textural parameters from pretreatment [(18)F]FDG PET/CT scans for the prediction of neoadjuvant radiation chemotherapy response and 3-year disease-free survival (DFS) in patients with locally advanced rectal cancer (LARC).
Methods: We performed a retrospective review of 74 patients diagnosed with LARC who were initially examined with [(18)F]FDG PET/CT, and who underwent neoadjuvant radiation chemotherapy followed by complete resection. The standardized uptake value (mean, peak, and maximum), metabolic volume (MV), and total lesion glycolysis of rectal cancer lesions were calculated using the isocontour method with various thresholds. Using three-dimensional textural analysis, about 50 textural features were calculated for PET images. Response to neoadjuvant radiation chemotherapy, as assessed by histological tumour regression grading (TRG) after surgery and 3-year DFS, was evaluated using univariate/multivariate binary logistic regression and univariate/multivariate Cox regression analyses.
Results: MVs calculated using the thresholds mean standardized uptake value of the liver + two standard deviations (SDs), and mean standard uptake of the liver + three SDs were significantly associated with TRG. Textural parameters from histogram-based and co-occurrence analysis were significantly associated with TRG. However, multivariate analysis revealed that none of these parameters had any significance. On the other hand, MV calculated using various thresholds was significantly associated with 3-year DFS, and MV calculated using a higher threshold tended to be more strongly associated with 3-year DFS. In addition, textural parameters including kurtosis of the absolute gradient (GrKurtosis) were significantly associated with 3-year DFS. Multivariate analysis revealed that GrKurtosis could be a prognostic factor for 3-year DFS.
Conclusion: Metabolic and textural parameters from initial [(18)F]FDG PET/CT scans could be indexes to assess tumour heterogeneity for the prediction of neoadjuvant radiation chemotherapy response and recurrence in LARC.
Keywords: 18F-Fluorodeoxyglucose; Metabolic volume; Positron-emission tomography; Prognostic parameter; Tumour heterogeneity; Tumour stage.