TY - JOUR T1 - Prognostic value of per-site metabolic tumor volume on FDG PET in patients with differentiated thyroid cancer before radioactive iodine therapy JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1700 LP - 1700 VL - 62 IS - supplement 1 AU - Yuko Uchiyama AU - Kenji Hirata AU - Shiro Watanabe AU - Shozo Okamoto AU - Tohru Shiga AU - Kazufumi Okada AU - Yoichi Ito AU - Kohsuke Kudo Y1 - 2021/05/01 UR - http://jnm.snmjournals.org/content/62/supplement_1/1700.abstract N2 - 1700Background: Although differentiated thyroid cancer (DTC) is generally a disease with a good prognosis, patients with large metabolic tumor volume (MTV) on FDG-PET tend to follow poor clinical courses. In DTCs, there are reports that neck lymph nodes have little effect on overall survival (OS), and also reports that the prognosis is poor when the patient has distant metastasis in uncommon sites such as liver and brain. Therefore, even if the volumes are equal, two metastatic lesions developed in two different sites may have different clinical impacts. However, the previous studies used whole-body MTV, and no study has focused on MTV evaluated by the metastatic site. We aimed to measure per-site MTV based on metastatic site and to test the prognostic performance of each per-site MTV.Methods: Based on the Transparent Reporting of Multivariate Prediction Model for Individual Prognosis or Diagnosis, this study is categorized as type 2a. In this IRB-approved retrospective study, 280 patients who received the first I-131 therapy from 2003 through 2014 at our hospital and presented with FDG-avid metastatic lesion were randomly split into training and validation datasets (N=190:90). The metastatic sites were classified as 1) neck lymph node, 2) distant lymph node, 3) lung, 4) bone, and 5) the other sites. These five per-site MTVs (MTVneck-node, MTVdistant-node, MTVlung, MTVbone, and MTVother-sites) were tested using univariate and multivariate analyses with Cox proportional hazard model in association with overall survival (OS). Using estimated weighting coefficients of per-site MTVs, a new index of ‘adjusted whole-body MTV’ (aMTV) was proposed. Using the validation dataset, aMTV was compared with conventional MTV (cMTV) in terms of the prediction of OS.Results: The characteristics of the included patients and average observation periods are summarized in the figure. As the result of univariate analysis of per-site MTV as a continuous variable to predict OS, p-values were 0.0763 (MTVneck-node), 0.0997 (MTVdistant-node), 0.3059 (MTVlung), 0.0060 (MTVbone), and 0.0011 (MTVother-site). And the result of univariate analysis of dichotomized MTVs which were using the best cutoff values searched by a 0.1 mL step, p-values were 0.0011 for MTVneck-node (best cutoff was 11.0mL), 0.0003 for MTVdistant-node (0.1mL), 0.0082 for MTVlung (1.5mL), 0.0062 for MTVbone(15.5mL), and 0.0002 for MTVother-sites (0.1mL). Based on the result of univariate analysis, MTVbone as continuous variables, while MTVneck-node, MTVdistant-node, MTVlung, and MTVother-sites as dichotomized variables, were used as input for multivariate analysis. The estimated weighting coefficient calculated as a result was 1.05 for dic(MTVneck-node), 0.86 for dic(MTVdistant-node), 0.73 for dic(MTVlung), 0.016 for MTVbone, and 2.10 for dic(MTVother-sites).Therefore, aMTV was expressed as 1.05×dic(MTVneck-node) + 0.86×dic(MTVdistant-node) + 0.73×dic(MTVlung) + 0.016×MTVbone + 2.10×dic(MTVother-sites), where dic(x) represents 0 or 1 based on a cut-off. In the model evaluation using the validation group, aMTV was a significant predictor of OS (p<0.0001) whereas cMTV was not (p=0.0633).Conclusion: In DTCs with FDG-avid metastasis before I-131 therapy, all per-site MTVs were significant predictors of patient prognosis. As aMTV outperformed cMTV to predict the prognosis, MTV should be recorded for each metastatic site. ER -