The application of 18F-FDG-PET/CT in gastric cancerstaging and factors affecting its sensitivity.

OBJECTIVE: To evaluate the accuracy offluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), to correctly determine initial tumor stage in treatment-naive gastric cancer patients and to analyze the factors influencing the risk of false negative results. SUBJECTS AND METHODS: The baseline 18F-FDG PET/CT scans of 111 previously untreated gastric cancer patients were retrospectively assessed. Sensitivity, specificity, positive (PPV) and negative prediction value (NPV) were evaluated. An array of clinical, pathological and metabolic variables was analyzed to identify factors contributing to the risk of a false positive (FP) and false negative (FN) PET/CT result in detecting primary and metastatic tumor sites. RESULTS: The sensitivity, specificity, PPV and NPV of PET/CT to visualize distant metastases were 76.4%; 86.7%; 83% and 81.2%, respectively. In 13 (11.7%) patients the PET/CT exam was able to identify metastatic sites not recognized in radiographic staging, significantly altering the initially planned management. Of 64 PET/CT studies negative for distant metastases, 12 (18.75%) were clinically confirmed to be false negative. The risk of acquiring a FN result for primary tumor was 10.8% (12/111) and the overall risk of any FN readout for either primary and metastatic sites was 18.9% (21/111). The factors that contributed to increased probability of a FN result for primary tumor detection were early primary tumor stage T1-T2 (+16.2%; χ2=5.0, P=0.025), female sex (+10.1%; χ2=5.71, P=0.017) and neutrophil count below 4.2k/µL (9.7%; χ2=6.1, P=0.014). Patients with non-intestinal Lauren histologic type (+18.7%; χ2=8.9, P=0.003) or signet-ring/mucinous carcinoma (+9.6%; χ2=7.7, P=0.005) had increased probability of PET/CT being unable to identify their distant metastases. Women and patients with low neutrophil count featured borderline insignificantly increased percentage of non-intestinal tumor histology (P=0.07 and P=0.057, respectively). CONCLUSION: Fluorine-18-FDG PET/CT is a valuable diagnostic method in gastric cancer patients which significantly contributes to determining the TNM stage and thus helps choose correct patient management. Histology and primary tumor stage as well as patient cohorts in which these factors may vary should be considered when evaluating results to decrease a chance of a false negative readout.

18-Fluorodeoxy-Glucose Positron Emission Tomography- Computed Tomography (18-FDG-PET/CT) for Gross Tumor Volume (GTV) Delineation in Gastric Cancer Radiotherapy

Purpose: Evaluation of the 18-fluorodeoxy-glucose positron emission tomography-computed tomography (18-FDGPET/ CT) for gross tumor volume (GTV) delineation in gastric cancer patients undergoing radiotherapy. Methods: In this study, 29 gastric cancer patients (17 unresectable and 7 inoperable) were initially enrolled for radical chemoradiotherapy (45Gy/25 fractions + chemotherapy based on 5 fluorouracil) or radiotherapy alone (45Gy/25 fractions) with planning based on the 18-FDG-PET/CT images. Five patients were excluded due to excess blood glucose levels (1), false-negative positron emission tomography (1) and distant metastases revealed by 18-FDG-PET/CT (3). The analysis involved measurement of metabolic tumor volumes (MTVs) performed on PET/CT workstations. Different threshold levels of the standardized uptake value (SUV) and liver uptake were set to obtain MTVs. Secondly, GTVPET values were derived manually using the positron emission tomography (PET) dataset blinded to the computed tomography (CT) data. Subsequently, GTVCT values were delineated using a radiotherapy planning system based on the CT scans blinded to the PET data. The referenced GTVCT values were correlated with the GTVPET and were compared with a conformality index (CI). Results: The mean CI was 0.52 (range, 0.12-0.85). In 13/24 patients (54%), the GTVPET was larger than GTVCT, and in the remainder, GTVPET was smaller. Moreover, the cranio-caudal diameter of GTVPET in 16 cases (64%) was larger than that of GTVCT, smaller in 7 cases (29%), and unchanged in one case. Manual PET delineation (GTVPET) achieved the best correlation with GTVCT (Pearson correlation = 0.76, p <0.0001). Among the analyzed MTVs, a statistically significant correlation with GTVCT was revealed for MTV10%SUVmax (r = 0.63; p = 0.0014), MTVliv (r = 0.60; p = 0.0021), MTVSUV2.5 (r = 0.54; p = 0.0063); MTV20%SUVmax (r = 0.44; p = 0.0344); MTV30%SUVmax (r = 0.44; p = 0.0373). Conclusion: 18-FDG-PET/CT in gastric cancer radiotherapy planning may affect the GTV delineation.