Detection of regional lymph metastasis with ¹⁸F-FDG PET/CT imaging in patients with rectal cancer

Objective: To evaluate the diagnostic value of ¹⁸F-FDG PET/CT imaging in detection of regional lymph node metastasis in patients with rectal cancer. Methods: A total of 48 patients (37 males, 11 females; average age 59.7 years) with rectal cancer who underwent preoperative PET/CT examination from May 2013 to May 2015 were enrolled. The long diameter, short diameter and SUV_max of lymph nodes on axial images were recorded. Metastatic lymph nodes (MLN) and non-metastatic lymph nodes (NMLN) were confirmed by postoperative pathology. Two-sample t test was used to compare the diameters and SUV_max between 2 groups; ROC curve was drawn to determine the optimal cutoff value and to assess the sensitivity, specificity, and accuracy of each index for differentiating MLN from NMLN. Results: A total of 739 lymph nodes were resected, 204 lymph nodes (88 MLN and 116 NMLN) were matched with those on PET/CT images. The long diameters of NMLN and MLN were (6.13 ± 1.94) mm and (8.49 ± 3.78) mm, respectively, and the short diameters were (4.73 ± 1.51) mm and (6.37 ± 2.57) mm, respectively(t = -5.788, -5.691, both P < 0.01). The SUV_max of NMLN and MLN were 1.13 ± 0.74 and 2.54 ± 1.76, respectively (t = -7.775, P < 0.01). For long diameter, short diameter and SUV_max, the ROC AUCs were 0.709, 0.731 and 0.851 respectively, the optimal cutoff values were 7.50 mm, 5.05 mm and 1.45 respectively, with the corresponding sensitivities of 54.5%(48/88), 67.0% (59/88) and 68.2% (60/88), specificities of 86.2% (100/116), 85.3% (99/116) and 87.9% (102/116), accuracies of 72.5% (148/204), 77.5%(158/204) and 79.4% (162/204). When a lymph node with SUV_max ≥ 1.45 or short diameter ≥ 5.05 mm was considered malignant, the sensitivity, specificity and accuracy were 84.1% (74/88), 83.6% (97/116) and 83.8% (171/204), respectively. Conclusions: ¹⁸F-FDG PET/CT imaging has significant value in detection of regional lymph node metastasis in patients with rectal cancer. The SUV_max ≥ 1.45 showed better diagnostic value than short diameter ≥ 5.05 mm and long diameter ≥ 7.50 mm. The highest diagnostic accuracy could be achieved, if SUV_max ≥ 1.45 or short diameter ≥ 5.05 mm is considered as the diagnostic criterion for lymph node metastasis. (authors)