Correlation Study Of Early Changes In Apparent Diffusion Coefficients And Radiosensitivity Of Human Nasopharyngeal Carcinoma Xenografts

ABSTRACT: Objectives: Our objective was to predict the radiosensitivity of humannasopharyngeal carcinoma xenografts in nude mice models with differentradiosensitivity through investigating the relationship between changes in apparentdiffusion coefficient （ADC） values based on diffusion-weighted imaging（DWI） andvolume changes related with radiotheraphy.Methods: Animal models of BALB/c-nu nude mice bearing human nasopharyngealcarcinoma xenografts were established respectively with CNE1or CNE2cell lines,whose radiosensitivities were quite different. Each cell line has20mice and was equallydivided into control and irradiation groups. Xenografts’ volumes were measured everyother day after tumor formation, mice in irradiation groups CNE1t and CNE2t werescanned with a diffusion-weighted imaging sequence, and the mean ADC values weremeasured （ADC₀）. Fifteen to20hours after tumors received15Gy, these mice werescanned and ADC values （ADC₁） were measured again. Mice in control groups CNE1cand CNE2c would not be irradiated, but were scanned and measured at the same time ofthe irradiation groups.Results: A mouse from the CNE1c group expired due to an anesthesia accident. ADC₀and ADC₁values of CNE1c、CNE1t、CNE2c、CNE2t groups were（1.708±0.458）×10^-3mm²/s、（1.684±0.441）×10^-3mm²/s，（1.705±0.522）×10^-3mm²/s、（1.603±0.250）×10^-3mm²/s，（1.297±0.623）×10^-3mm²/s、（1.049±0.260）×10^-3mm²/s，（1.647±0.312）×10^-3mm²/s、（0.847±0.306）×10^-3mm²/s. ADC₁values were muchmore smaller than ADC₀in CNE2t group, but there were no statistical differencesbetween ADC₀and ADC₁in the other three groups（P values were0.699,0.575,0.212respectively）. ADC_1-0and ΔADC of CNE1c and CNE1t groups were（-0.240±1.902）×10^-4mm²/s（,-1.017±5.215）×10-4mm²/s and（-0.727±12.175）%（,1.221±32.074）%. All ADC values of CNE1c group and CNE1t group exhibited no statistically significant difference （P values were0.989,0.635,0.682and0.867respectively）. ADC_1-0and ΔADC of CNE2c group and CNE2t group were（-2.480±5.844）×10^-4mm²/s（-7.994±3.827）×10^-4mm²/s（,-6.527±43.944）%（-46.739±22.816）%，the differencesof ADC₀and ADC₁from these two groups were not statistically significant（both Pvalues were0.130）, but ADC_1-0and ΔADC values exhibited statistically significantdifferences（P values were0.022and0.019）. Compared CNE1c with CNE2c, therewere significant statistical difference in ADC₁values of the two groups（t=3.924，P=0.001）, but differences of ADC₀, ADC_1-0and ΔADC values were not statisticallysignificant（P values=0.110,0.264and0.696）; While the differences of ADC₀values inCNE1t and CNE2t were not statistically significant（t=0.300，P=0.768）, there werestatistically significant differences in ADC₁, ADC_1-0and ΔADC values（P values were﹤0.001、0.004and0.001,respectively）. From the fourth day after irradiation, thedifferences of δVxfrom two irradiation groups were statistically significant（all P valueswere less than0.001）. From the second day on after irradiation, there was a negativecorrelation between δVxand ΔADC values, and a positive correlation between δVxandcell lines from the fourth day on. With multiple linear regression analysis, we found thatboth ΔADC values and cell line type were influence factors from fourteenth on.Conclusions: This study found that ADC values of xenografts with differentradiosensitivity changed differently; Changes of ADC values before and after irradiationwas influence factor of volume changes correlated with irradiation. Therefore,ADCvalues are able to predict the radiosensitivity of nasopharyngeal carcinoma, the range ofearly ADC values decrease bigger and its radiosensitivity is higher.