Significant value of 18F-FDG-PET/CT in diagnosing small cervical lymph node metastases in patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy

Background: Little is known about the nature of metaistasis to small cervical lymph nodes(SCLNS) in the patients with nasopharyngeal carcinoma(NPC)examined by using 18-fluoro-2-deoxy-glucose(^(18)F-FDG) positron emission tomography/computed tomography(PET/CT).The present study aimed to evaluate the diagnostic values of PET/CT in identifying metastasis in SCLNs in NPC patients.Methods: Magnetic resonance images(MRI) and PET/CT scans for 470 patients with newly diagnosed, non-distant metastatic NPC were analyzed. Metastatic rates of SCLNs were defined by the positive number of SCLNs on PET/CT scans and total number of SCLNs on MRI scans. Receiver operating characteristic curve was applied to compare PET/CT-determined stage with MRI-determined stage.Results: In total, 2082 SCLNs were identified, with 808(38.8%) ≥ 5 and < 6 mm in diameter(group A), 526(25.3%)≥ 6 and < 7 mm in diameter(group B),374(18.0%)≥ 7 and < 8 mm in diameter(group C), 237(11.4%) ≥8 and<9 mm in diameter(group D),and 137(6.5%) ≥ 9 and <10 mm in diameter(group E).The overall metastatic rates examined by using PET/CT for groups A, B,C,D, and E were 3.5%, 8.0%, 31.3%, 60.0%, and 83.9%, respectively(P< 0.001). In level IV/Vb, the metastatic rate for nodes ≥ 8 mm was 84.6%. PET/CT examination resulted in modification of N category and overall stage for 135(28.7%) and 46(9.8%) patients, respectively. The areas under curve of MRIdetermined and PET/CT-determined overall stage were 0.659 and 0.704 for predicting overall survival, 0.661 and 0.711 for predicting distant metastasis-free survival, and 0.636 and 0.663 for predicting disease-free survival.Conclusions: PET/CT was more effective than MRI in identifying metastatic SCLNs, and the radiologic diagnostic criteria for metastatic lymph nodes in level IV/Vb should be re-defined.

A model System for Validation of PET Radiopharmaceuticals: Focusing on Tumor Microenvironment

Positron emission tomography (PET) imaging has emerged as an important clinical tool for cancer management, and specifically targeted radiopharmaceuticals play critical roles on PET molecular imaging. Solid cancers have highly complex and heterogeneous microenvironment, this review focused on those microenvironmental factors such as hypoxia, proliferation and perfusion and, accordingly, a novel test system for validation of current and novel targeted imaging radiopharmaceuticals. In this review, we have introduced the establishment of cancer and metastases models in nude mice, visualization of microenvironmental components of hypoxia, proliferation, perfusion, stroma and necrosis in cancers and metastases for establishing the microenvironment based model system, and validation of several radio- pharmaceuticals such as 18F-fluoro-2-deoxyglucose (18F-FDG) 18F-fluorothymidine (18F-FLT), 18F-misonidazole (18F- FMISO) using the system. We found that 18F-FLT accumulates in proliferating cancer cells, while 18F-FMISO and 18F-FDG mostly accumulate in hypoxic and non-proliferative cancer cells, 18F-FDG shares roughly similar intratumoral distribution pattern with 18F-FMISO and IAZGP, but mutually excludes 18F-FLT. This model system validated current tracers for imaging glucose metabolism, hypoxia and proliferation in cancer and metastases, therefore, can be used for novel targeted radiopharmaceuticals validation.