Diagnostic and prognostic value of quantitative 18F-FDG PET/CT metabolic parameters combined with clinical indicators in patients with locally recurrent rectal cancer.

Purpose: To evaluate the diagnostic and prognostic value of quantitative ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) metabolic parameters combined with clinical indicators in patients with locally recurrent rectal cancer (LRRC).

Materials and methods: The quantitative ¹⁸F-FDG PET/CT metabolic parameters and clinical indicators of all patients with suspected LRRC after curative resection of rectal or distal sigmoid colon cancer were retrospectively analyzed. The sensitivity, specificity, and accuracy of ¹⁸F-FDG PET/CT metabolic parameters were assessed using receiver operating characteristic (ROC) curves. Kaplan-Meier (KM) analysis and log-rank tests were used to estimate overall survival (OS). Univariable and multivariable Cox regression models were used to determine the potential predictors of OS.

Results: A total of 92 patients were included, with 59 confirmed LRRC cases and 33 benign lesions. Among all parameters, maximum standardized uptake value (SUV_max) demonstrated the highest diagnostic performance for LRRC (cut-off = 4.71 g/mL, AUC = 0.923, sensitivity = 93.22%, specificity = 84.85%, accuracy = 90.22%). In comparison, total lesion glycolysis of the local lesion (TLG_local) exhibited relatively lower efficacy (cut-off = 33 g, AUC = 0.785, sensitivity =77.97%, specificity = 72.73%, accuracy = 76.09%). KM survival analysis revealed that TLG_local > 33 g was significantly associated with shorter OS (p = 0.001). Multivariable Cox analysis identified TLG_local > 33 g (HR = 3.62, 95% CI: 1.39-9.44, p = 0.008), sacral involvement (HR = 2.68, 95% CI: 1.13-6.37, p = 0.025), and surgical resection (HR = 0.19, 95% CI: 0.06-0.66, p = 0.009) as independent prognostic factors for OS.

Conclusion: ¹⁸F-FDG PET/CT metabolic parameters demonstrated significant diagnostic and prognostic value in the setting of suspected LRRC. SUV_max exhibited the highest diagnostic accuracy for LRRC, and TLG_local was an independent predictor of OS.

Clinical relevance statement: This study highlights the diagnostic and prognostic value of ¹⁸F-FDG PET/CT metabolic parameters in locally recurrent rectal cancer (LRRC). Maximum standardized uptake value shows high diagnostic accuracy, and total lesion glycolysis of the local lesion serves as both a diagnostic and prognostic marker for risk stratification. Additionally, sacral involvement and surgical treatment are independent predictors of overall survival. These findings underscore the importance of integrating metabolic parameters into clinical practice to enhance early detection and assist in treatment decision-making for patients with suspected LRRC.