Diagnostic value of FDG-PET/CT for lateral pelvic lymph node metastasis in rectal cancer treated with preoperative chemoradiotherapy.

BACKGROUND: The aim of this study was to elucidate the diagnostic value of 18 F-fluorodeoxyglucose positron emission tomography (PET)-computed tomography (CT) for lateral pelvic lymph node (LPN) metastasis in rectal cancer treated with preoperative chemoradiotherapy (CRT).

METHODS: Eighteen rectal cancer patients with enlarged (≥ 8 mm) LPNs were treated with CRT followed by total mesorectal excision with LPN dissection during 2012-2015. After CRT, LPN maximum standard uptake values (SUVmax) were measured using PET/CT and long diameters of LPNs were measured using CT or magnetic resonance imaging (MRI). LPN size and SUVmax were compared with pathological status in the resected specimen. Radiologically identified nodes were matched with surgically resected nodes by separate examination of 4 lymph nodal regions: internal iliac, obturator, external iliac and common iliac lymph nodes.

RESULTS: In total, 34 LPNs were located by CT or MRI. Metastatic LPNs were significantly larger than non-metastatic LPNs (size, mean ± standard deviation: 13.0 ± 8.3 vs. 4.9 ± 3.5 mm, p < 0.01). SUVmax was determinable for 28 of the LPNs, among which metastatic LPNs were found to have significantly higher SUVmax than non-metastatic LPNs (mean ± standard deviation: 2.2 ± 1.3 vs. 1.2 ± 0.3, p < 0.01). Receiver operating characteristic analysis suggested optimal cutoff values of size = 12 mm which had an accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 82.1, 70.6, 100, 100, and 68.8%, respectively. An SUVmax = 1.6 had an accuracy, sensitivity, specificity, PPV, and NPV of 85.7, 76.5, 100, 100, and 73.3%, respectively. When LPNs that were ≥ 12 mm in size and/or had an SUV ≥ 1.6, the accuracy, sensitivity, specificity, PPV, and NPV were 92.9, 88.2, 100, 100, and 84.6%, respectively.

CONCLUSIONS: After CRT, PET/CT alone or in combination with CT and MRI can predict the presence of metastatic LPN with a high degree of accuracy. PET/CT may be useful in selecting patients with rectal cancer who would benefit from LPN dissection in addition to TME. These results need to be confirmed by larger studies.