Abstract
3021
Introduction: 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is a noninvasive procedure that allows assessment of glucose metabolism. A semi-quantitative parameter is SUVmax (maximum standardized uptake value) is one of known prognostic parameter; however this indicates only single voxel value and not metabolism of whole. MTV (metabolic tumor volume) is calculated using various thresholds (40% of the tumor SUVmax or SUV cut off of 2.5). Utility of MTV as prognostic marker is proven in esophageal cancer, head and neck cancers. In continuation to this we tried to find correlation of metabolic tumor volume of primary gallbladder carcinoma based on fixed relative threshold (MTV40, i.e. 40% of SUVmax) and fixed absolute threshold method (MTV2.5, i.e. SUV of 2.5) of baseline FDG-PET/CT with the overall survival in cases of locally advanced Gallbladder carcinoma (GBC).
Methods: A total of 32 patients of confirmed GBC who were referred for FDG- PET/CT from September 2018 to May 2020 were included in this retrospective study. The locally advanced GB lesions were defined as T3-T4 GB lesion or invasion of adjacent structures or regional nodal metastasis. Cases with distant metastases, insufficient medical records, and patients who have received cancer directed systemic therapy were excluded. PET VCAR (Volume Computer Assisted Reading) software was used to calculate metabolic tumor volume of primary tumor (MTV) based on fixed absolute threshold method (MTV2.5, i.e. SUV of 2.5) and fixed relative threshold (MTV40 i.e. 40 % of SUVmax). All patients were treated with chemotherapy. For evaluation of treatment response was based on follow up CT or PET/CT whichever available. If follow up imaging is not available then clinical records or last follow up visit was considered.
Statistical analysis: -
Overall survival was defined as duration between date of diagnosis to date of death due to any cause or date of last follow up. Kaplan-Meier method was used for the estimation of the probability of Overall survival (OS). Univariate analysis was performed with log-rank test. The maximally selected rank statistics from the 'maxstat' R package was used to determine cut point for variables. All tests were 2 tailed and significance set at p<0.05, the MTV was reported with 95% confidence intervals (CI). Analysis was performed using R version 3.4.2, from the Comprehensive R Archive Network (R Core team, 2020).
Results: In our study, data of 32 patients was analyzed. The average duration of follow up was 5.8 months. ON folow up 12/32 patients died ( average duration of follow up 5 months). 10 patients were detected with disease progression (average duration of follow up 5.5 months). Rest of patients showed response to treatment or stable disease. Cutoff of metabolic tumor volume of primary tumor based on fixed absolute threshold method (MTV2.5) was found to be 272.35 and for fixed relative threshold method (MTV40), it was 67.83. Six (06) months and 1year survival percentage of patients with MTV more than 272 was found to be 54 % & 36 % compared to 87 % & 81 % survival percentage for patients with MTV less than 272 respectively. The MTV2.5 of primary tumor was found to be prognostically significant (p<0.05). The MTV40 of primary tumor did not correlate with overall survival.
Conclusions: In our study, there appears correlation between fixed absolute threshold method based metabolic tumor volume of primary gallbladder tumor (MTV2.5) with the overall survival in cases of locally advanced gallbladder carcinoma. Therefore, MTV2.5 can be used routinely for identifying patients with poor prognosis and further clinical management. For MTV40, further data and analysis is required before any conclusion.
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