Association of intra-individual heterogeneity of volumetric parameters or texture features and chemotherapeutic response on FDG PET in patients with malignant lymphoma

Objectives: Some lymphoma patients (pts) with multiple lesions achieve complete response (CR), while others do not. In the present study, we clarified that the intra-individual heterogeneity of volumetric parameters (VPs) or texture features (TFs) on FDG PET had association with treatment response after chemotherapy (Cx) in pts with follicular lymphoma (FL), comparing results with evaluation in the representative lesion in each pt. Methods: 30 FL pts having pre- and postCx FDG PET/CT exams were included in this study. They had multiple lesions before Cx. Two lesions at the preCx exam were selected in each pt. The 1st lesion was the one showing residual activity at the postCx exam or the largest lesion in case of CR. The 2nd lesion was the largest one other than the 1st lesion without residual activity at the postCx exam. VPs and TFs were obtained from a 3D ROI covering the 1st and 2nd lesions separately. Metabolic tumor volume and total lesion glycolysis were calculated as VPs. TFs evaluated in this study included entropy, homogeneity, low-, high gray-level zone emphasis, short-, and long-run emphasis as recommended by Orlhac, et al (JNM 2014). Intra-individual heterogeneity was evaluated using VP and TF values with following parameters: difference of the values (D), difference of the values divided by mean values (D/M). These parameters as well as values in the 1st lesions were evaluated as to treatment response, i.e. CR or not, which was determined with Lugano classification using postCx PET results. The values in the 1st lesions were compared each other and their variation was calculated with coefficient of variance (CV). Results: 19 and 11 pts showed CR and non-CR, respectively, after Cx. In the 1st lesions, VPs strongly correlated with entropy, homogeneity, short-, and long-run emphasis (Spearman's |Rho| >0.8), while SUVmax had no strong correlation with TFs. CV was small in TFs (0.01 - 0.33) and SUVmax (0.47) as compared to VPs (1.12). Similar tendency was observed in the 2nd lesions. D or D/M for intra-individual heterogeneity was not different between CR and non-CR pts, while low gray-level zone emphasis (LGZE) in the 1st lesions was larger in CR than non-CR pts with a statistical significance (0.064 vs. 0.051, p