Advantage of PET/CT in Target Delineation of MRI-negative Cervical Lymph Nodes In Intensity-Modulated Radiation Therapy Planning for Nasopharyngeal Carcinoma

Abstract

Introduction: In intensity-modulated radiation therapy (IMRT) planning for nasopharyngeal carcinoma (NPC), cervical lymph nodes (CLNs) that appear negative on magnetic resonance imaging (MRI) scans can be difficult to target. The purpose of this study was to assess the advantage of 18F-fluorodeoxyglucose positron emission tomography with computed tomography (18F-FDG PET/CT) for distinguishing MRI-negative CLNs and the effect of 18F-FDG PET/CT on diagnosis, target delineation, and dose prescription in IMRT planning for NPC.Methods: Thirty-five NPC patients with 37 MRI-negative CLNs underwent 18F-FDG PET/CT imaging before treatment. Ultrasonography-guided fine-needle aspiration cytology (USgFNAC) was performed to examine the pathology of CLNs. The 18F-FDG PET/CT and cytopathological results were compared, and the diagnostic accuracy of 18F-FDG PET/CT was calculated. The cytopathologically confirmed CLNs were delineated and treated as the gross tumor volume of lymph nodes (denoted as GTVnd).Results: Nineteen of the 37 MRI-negative CLNs were positive on 18F-FDG PET/CT, and metastasis was confirmed by USgFNAC in 16 CLNs. Of the remaining 18 18F-FDG PET/CT-negative lymph nodes, metastasis was confirmed in one. The diagnostic accuracy, sensitivity, and specificity of 18F-FDG PET/CT were 89.2%, 94.1%, and 85.0%, respectively. The positive and negative predictive values were 84.2% and 94.4%, respectively. With a median follow-up of 48.3 months, no relapse was observed among the 18F-FDG PET/CT-positive CLNs with metastasis confirmed by USgFNAC and treated as GTVnd.Conclusion: 18F-FDG PET/CT had high accuracy, sensitivity, and specificity for distinguishing MRI-negative CLNs. 18F-FDG PET/CT-positive CLNs could reasonably be categorized as high-risk clinical tumor volume in IMRT planning for NPC.

A Head-to-Head Comparison of 68Ga-DOTA-FAPI-04 and 18F-FDG PET/MR in Patients with Nasopharyngeal Carcinoma: A Prospective Study

“…Figure 1 shows the images of four representative patients. Primary tumor uptake was higher in 18 F-FDG (SUVmax 17.73 ± 6.84) than 68 Ga-FAPI (SUVmax 13.87 ± 5.13), but no signi cant differences were found (P =0.078, Table 2). We further compared the correlation between the uptake of two tracers and found that the SUVmax of 68 Ga-FAPI had no relationship with 18 F-FDG (r =0.227, p=0.416, Figure 2A).…”

“…Primary tumor uptake was higher in 18 F-FDG (SUVmax 17.73 ± 6.84) than 68 Ga-FAPI (SUVmax 13.87 ± 5.13), but no signi cant differences were found (P =0.078, Table 2). We further compared the correlation between the uptake of two tracers and found that the SUVmax of 68 Ga-FAPI had no relationship with 18 F-FDG (r =0.227, p=0.416, Figure 2A). The T staging of 68 Ga-FAPI was consistent with the MRI ndings in all the patients, but the T staging in one of the patients was underestimated by 18 F-FDG (Table 1).…”

“…Both 18 F-FDG and 68 Ga-FAPI PET acquisitions were performed in 3D with a 10-min/bed position (DFOV=30 cm) during MR acquisition. The PET datasets were reconstructed with a 192×192 matrix (pixel size: 1.5625×1.5625×2.78 mm 3 ) with TOF and point spread function (PSF)-ordered subset expectation maximization (OSEM) algorithms with 28 subsets and three iterations, followed by a 3-mm Gaussian lter.…”

“…The acquired PET and MR images were sent to the AW workstation (AW4.6, GE Healthcare, USA) for registration, fusion, and measurement. Both 18 (2) N staging assessment: On MR images, the diagnosis of metastatic lymph nodes should satisfy at least one of the following criteria: (a) necrosis or extracapsular spread was observed, (b) the shortest axial diameter was ≥5 mm in the retropharyngeal region or ≥10 mm in other regions, (c) there was a cluster of three or more lymph nodes of borderline size [14]. On PET images, if 18 F-FDG or 68 Ga-FAPI uptake exceeded the surrounding tissue, it was regarded as a positive lymph node uptake.…”

“…We further compared the correlation between the uptake of two tracers and found that the SUVmax of 68 Ga-FAPI had no relationship with 18 F-FDG (r =0.227, p=0.416, Figure 2A). The T staging of 68 Ga-FAPI was consistent with the MRI ndings in all the patients, but the T staging in one of the patients was underestimated by 18 F-FDG (Table 1).…”