Purpose: Induction chemotherapy (IC) is an effective way to control subclinical metastasis in locally-advanced nasopharyngeal cancer patients. If the outcome can be predicted at an early stage of the treatment, the patient could be spared from unnecessary treatment.^1,2,3 In this light, the aim of the present study is to find appropriate metrics for assessing adenopathy’s response through quantification of the heterogeneity in diffusion-weighted images (DWI) of lymph nodes (LN) early after initiation of IC. Subjects/Method: The study group consisted of 7 patients. DWI was performed before and ten days after the initiation of injection in the first cycle of induction chemotherapy on 1.5T Avanto Siemens scanner. Patient characteristic and imaging parameters has shown in Table1, 2. Apparent diffusion coefficient (ADC) maps were generated from DW images on the system workstation. LNs, diagnosed as malignant on pre-therapeutic clinical and imaging assessment, were included for response assessment. Regions of interest (ROIs) containing the malignant LNs were delineated on the ADC-maps and Gd-enhanced T1-weighted images for each patient at two different time points. The LN volumes were calculated for selected area on T1C images. Several commonly-used quantitative parameters, including mean-, max-, min-, and median-ADC were calculated for defined ROIs on ADC map. Moreover, first-order histogram analysis was applied on the ROIs to derive the following features: (1) histogram standard deviation, representing average contrast, (2) normalized variance, as a measure of smoothness, (3) skewness, denoting the third moment, (4) energy, as a measure of uniformity or homogeneity, and (5) entropy, a statistical measure of irregularities of ADC-values. Result: For each quantitative parameter, differences between two time-points were compared with Willcoxon none parametric test. A level of p-value less than 0.05 was regarded as statistically significant. As indicated in Table3, Mean, Median, smoothness, third moment and uniformity are parameters indicate statistically significant difference (p value< 0.05) for early changes of LNs structure following induction chemotherapy. there weren’t any significant change in LN’s Volume (p-value = 0.128). Uniformity metric decreased in second time-point (after IC) for all patients.

Discussion/Conclusion: For nasopharyngeal patient with involved LN, the standard determination of LN’s response is conventional MRI. In this study, histogram analysis on ADC map was carried out on manually defined ROI within the tumor to reveal physiological aterations early after IC. For this purpose, several quantitative metrics derived from ADC-map were explored to obtain the most accurate feature(s) as potential predictive biomarker for early response of the lymphnode to IC. The initial results showed that mean, smoothness, third moment and uniformity metrics, which are indicators of heterogeneity, could detect early response of the Lymph node to treatment. While the change in lymph nodes volume did not exhibit significant difference (p-value: 0.128) for early response assessment. Finally, the results reported in this abstract will be validated in a larger patient population to determine which heterogeneity metrics can be adopted as relevant biomarkers for response of Lymph node to IC. Serial DWI will be acquired to find correlation between changes of extracted heterogeneity metrics and the tumor residue after completion of the IC. .