The Analysis Of Dynamic Change Of Apparent Diffusion Coefficient Values In Human Nasopharyngeal Carcinoma Xenografts After Irradiation And Its Correlation With Histologic Features

Objective To analyze the differences of dynamic change inapparent diffusion coefficient（ADC） values on human nasopharyngealcarcinoma xenografts with different radiosensitivity after irradiationand the correlation between ADC values and tumor cellularity, necrosispercentage,KI67scores. Materials and Methods BALB/c-nu nude mice （n=70） were divided into2groups that were subcutaneously injected withhighly differentiated human nasopharyngeal squamous cell carcinoma cellline（CNE-1） or poorly differentiated nasopharyngeal squamous cellcarcinoma cell line（CNE-2）. Each group was further divided into controlgroup （Group C, n=5） and therapy groups （Group T, n=30）. Group T receivedradiotherapy at a single fraction of15Gy. According to different timepoints （1day,2days,3days,5days and7days after irradiation）, groupT then divided into5sub-groups,6nude mice in each group. All casesreceived MR-DWI scans prior to irradiation and group T received MR-DWIscans at the time points mensioned above. ADC values of the xenograftswere measured on ADC maps with the method of margin-outline whole-partmeasurement. ADC₀, ADC₁, ADC₂, ADC₃, ADC₅, ADC₇were used to respectivelysymbolize the ADC values prior to as well as1day,2days,3days and7days after irradiation. Change in ADC values before and afterirradiation was defined as ΔADC. ΔADC₁，ΔADC₂，ΔADC₃，ΔADC₅and ΔADC₇were used to symbolize ΔADC of each time point（ΔADC₁=（ADC₁-ADC0）/ADC0*100%and others so on）. Specimens of all tumors were stained withHE and KI67. Image J software was used to calculate the tumor cellularity,necrosis percentages and KI67scores. SPSS17.0software was adopted toanalyze the experimental data. Statistical significance was defined bya P value of0.05. Results The ADC0of CNE-1and CNE-2groups were 1.488±0.284*10^-3mm²/s and1.273±0.259*10^-3mm²/s, respectively （t=-3.312，P=0.001）. One-way ANOVA showed that the differences of ADC valuesbetween6sub-groups and ΔADC between5sub-groups in CNE-2group werestatistically significant （ADC: F=10.753，P<0.001; ΔADC: F=11.282，P<0.001）, while which in CNE-1group were not（ADC:F=1.996，P=0.109; ΔADC:F=2.703，P=0.053）. The differences of ADC₂，ΔADC₁and ΔADC₇between CNE-1and CNE-2groups were statistically significant （ADC₂：t=-11.538，P<0.001；ΔADC₁：t=-3.701,P=0.004；ΔADC₇：t’=3.720,P=0.008）. Partial correlationanalysis showed that there was no correlation between ADC values or ΔADCand KI67scores（P value were0.062and0.627, respectively）.With thePearson correlation analysis, ADC values correlated significantly withtumor cellularity （r=-0.613, P<0.001）, necrosis percentage（r=0.554,P<0.001）; and ΔADC also correlated significantly with tumor cellularity（r=-0.623, P<0.001）, necrosis percentage（r=0.567, P<0.001）. ConclusionThere exist marked differences in initial ADC values and dynamic changeof ADC values after irradiation on human nasopharyngeal carcinomaxenografts with different radiosensitivity. The change of ADC values mayhelp to reflect the variation in microstructure of tumor after irradiation,which could be one of the possible mechanisms of DWI being used inpredicting radiosensitivity of nasopharyngeal carcinoma.