Investigation of intratumoral heterogeneity in nasopharyngeal carcinoma: a distinct role of PET-CT from MRI

Abstract

Tumors are heterogeneous due to cellular proliferation, necrosis, noncellular accumulations and physiologic characteristics, etc. It has been reported that heterogeneity is related to outcome, and studying its evolution may help to optimize treatment planning. We aimed to study the role of tumor heterogeneity reflected by PET-CT in the diagnosis of Nasopharyngeal Carcinoma (NPC), a leading cancer type in South China, and the correlation with MRI findings. It was hypothesized that tumor heterogeneity reflected by PET-CT correlated with both NPC diagnosis (SUVmax, tumor volume, stage, etc) and heterogeneity reflected by MRI scanning. A total of 26 newly-diagnosed NPC patients who had received both PET-CT and MRI examinations (interval between PET-CT and MRI scans not longer than two weeks) with the tumor size bigger than 1.5cm in any direction were studied. Intratumoral heterogeneity was calculated by taking the derivative (dV/dT) of the volume-threshold function in PET-CT images of the whole tumor. The relationship between intratumoral heterogeneity and NPC diagnosis (SUVmax, tumor volume, staging, etc) was determined for this cohort. To study the correlation between the findings of MR and PET, MR images, including T1W, T2W, post-contrast T1W images were registered to PET images by using the software SPM 5 or FSL. Voxel-based correlation between signal intensity in registered MR and PET images was performed for each patient within the ROI automatically drawn in PET applying a threshold of 40% SUVmax. It was found that the heterogeneity reflected by PET significantly correlated with tumor volume, M-stage, AJCC stage, and SUVmax (p<0.05); but not with T-stage (p=0.069) and N-stage (p=0.063). However, only in part of this cohort, significantly positive or negative correlation was found (9 in 26 cases, between T1W and PET; 19 in 26, between T2W and PET; 13 in 26, between post-contrast T1W and PET), with weak correlation coefficients (-0.2060.439). In conclusion, the intratumoral heterogeneity of FDG uptake has significant correlation with tumor volume, SUVmax and staging, but no or weak relationship with heterogeneity of MRI signal intensity and contrast enhancement. This finding may help to improve the characterization of NPC, while the value of intratumoral heterogeneity in NPC prognosis remains to be studied.