The Value Of Baseline ¹⁸F-FDG PET Metabolic Parameters In The Prognostic Evaluation Of Diffuse Large B-cell Lymphoma

Objective:Diffuse large B-cell lymphoma（DLBCL）is the most common hematological malignancy.Due to the heterogeneity of the disease itself in terms of biological characteristics,the prognosis of patients is also different.It is very important to find out the biological and imaging indicators that accurately reflect the patient’s disease state and tumor burden,and to identify poor survival outcomes early.This study was conducted to investigate the clinical parameters,existing criteria for evaluation of prognosis,and the value of baseline ¹⁸F-FDG PET metabolic parameters,including Metabolic tumor volume（MTV）and Total original glycolysis（TLG）,on evaluation of prognosis in patients with DLBCL.Methods:We retrospectively analyzed the data of 50 patients who were pathologically confirmed as DLBCL in Taizhou People’s Hospital from January 2016 to December 2020.All patients underwent ¹⁸F-FDG PET/CT examination at the time of initial diagnosis and received first-line chemotherapy.The clinical parameters of patients at baseline,including gender,age at first diagnosis,Eastern Cooperative Oncology Group（ECOG）performance status score,Ann Arbor stage,lactate dehydrogenase（LDH）level,the number of extranodal lesions,and the expression level of cell proliferation nuclear antigen（Nuclear-associated antigen,Ki-67）,were collected.International Prognostic Index（IPI）and Improved International Prognostic Index（National Comprehensive Cancer Network-International Prognostic Index,NCCN-IPI）were used to score patients’prognostic risk.All baseline PET/CT images were analyzed.Three methods of standardized uptake value（SUV）equal to 2.5,4 or 41%of the maximum standardized uptake value（SUVmax）as the threshold for delineating the Region of interests（ROIs）were used and the metabolic parameters were collected,which were defined as MTV2.5,MTV4,MTV41%and TLG2.5,TLG4,TLG41%.According to the results of follow-up,remission and stable disease were defined as the good prognosis group,and relapse,progression or death were defined as the poor prognosis group.The chi-square test was used to compare the clinical parameters and the prognostic differences among different risk groups based on the existing prognostic evaluation criteria.Through Receiver operating characteristic curve（ROC）,the optimal cut-off value of metabolic parameters obtained from ROIs drawn by various thresholds were determined,and the area under the curves（AUCs）were compared.Kaplan-Meier survival analyses on cut-off value in each group were performed,and the differences between the survival curves were compared by log-rank test.Finally,Cox risk regression model was used for multivariate analysis of significant prognostic factors.Results:1.Patients follow-up:Fifty patients were followed up for 5-60 months,and the median follow-up time was 17.5 months.Thirty-three patients had a good prognosis;17patients had a poor prognosis,of which 16 had recurrence or progression,and 1 died of lymphoma-related symptoms.2.Prognostic analysis of clinical parameters:Among the Ann staging and the number of extranodal lesions,the incidence of poor prognosis in the high-risk group was significantly higher than that in the low-risk group（P=0.028,P=0.010）.The remaining clinical parameters had no significant correlation with the prognosis.3.The prognostic analysis of the existing prognostic evaluation standards:The incidence of poor prognosis in the high-risk group based on the IPI score was significantly higher than that in the low-risk group（P=0.022）,however the NCCN-IPI score had no significant correlation with the prognosis.4.Prognostic analysis of baseline PET/CT metabolic parameters:The metabolic parameters obtained from ROI were delineated by three thresholds,all of which could distinguish the group with good prognosis from the group with poor prognosis.The MTV and TLG of patients in the poor prognosis group were significantly higher than those in the good prognosis group,and the difference was statistically significant（all P<0.05）.ROC analysis results showed that the optimal cut-off values of MTV2.5 and TLG2.5 were 249.65cm3 and 1183.18g（AUC:0.80,0.793）,the cut-off values of MTV4and TLG4 were 125.95 cm3 and 956.35g（AUC:0.818,0.813）,the cut-off values of MTV41%and TLG41%were 63.2 cm3 and 935.74g（AUC:0.742 and 0.747）,respectively.The P values of all cutoff values were<0.05,indicating high diagnostic efficiency.Comparing the AUC value of each cut-off value,it is found that the AUC value of MTV4 is the largest,and the prognostic performance is the best.For the same metabolic parameters,the incidence of adverse outcomes was higher in the group of‘higher than the cut-off value’,and the difference between the groups was statistically significant（P<0.05）.Kaplan-Meier survival analysis shows that the best cut-off values derived from the three thresholds delineating ROI can better distinguish survival outcomes,patients of‘less than the cut-off value’had a higher 2-year PFS rate（all P<0.05）.5.Multivariate analysis of prognosis:Ann stage,number of extranodal lesions,IPI score,and MTV4 were included in multivariate analysis.The results showed that MTV4is an independent predictor of PFS in DLBCL patients（P=0.007）,with a Hazard Ratio（HR）of 17.612.Other factors are not independent factors of PFS in DLBCL patients.Conclusion:1.Ann stage,number of extranodal lesions in clinical parameters,and IPI in existing prognostic evaluation criteria are related to patient prognosis.2.The best cut-off values of MTV and TLG obtained by three different thresholds delineating ROI can effectively judge the prognosis of patients and can predict the2-year PFS.The MTV4 cut-off value has the best diagnostic performance.When the baseline MTV value is higher than the cut-off value,it indicates that the patient has a poor prognosis.3.In the multivariate analysis,only MTV4 was an independent predictor affecting the prognosis of DLBCL patients.