Application Of Diffusion-weighted Magnetic Resonance Imaging In Radiotherapy Of Nasopharyngeal Carcinoma

ObjectiveThe study was to evaluate the application of diffusion-weighted magnetic resonance imaging (DW-MRI) in the radiotherapy of nasopharyngeal carcinoma (NPC).Methods1.38 patients with NPC, whose the routine MRI and DW-MRI were performed before the radiotherapy.A comparison of the MRI manifestation of the T-staging and lymph nodes metastasis of the NPC with the ADCs was performed, and the sigal of the primary tumor and metastatic lymph nodes was observed.2.This study involved 15 patients suffering from nasopharyngeal carcinoma treated with radiotherapy. All patients passed the examinations of the routine MRI and DW-MRI before radiotherapy and at accumulative dose of 10Gy,20Gy or 40Gy separately after radiotherapy. The changes of the size, the signal of DW-MRI and the mean apparent diffusion coefficient (ADC) with the primary tumor and metastatic lymph nodes were compared.Results1.The maximum area of the primary tumor in the DW-MRI is significantly smaller than that in the fat-suppression T1 WI before radiotherapy (P<0.05), but the difference of the maximum area of the metastatic lymph nodes was not statistically significant((P =0.066); The difference of the ADCs between group T1+T2 and group T3+T4 in the primary tumor of the NPC or the cervical lymph nodes metastasis and the retropharyngeal nodes metastasis were not statistically significant (P>0.05). The mean ADC value of the cervical lymph nodes metastasis (≥3cm) was 0.703±0.026 X 10-3mm2/s, in the cervical lymph nodes metastasis (<3cm) was 0.735±0.020 X 10"3mm2/s, the difference was statistically siganificant (P>0.05)2.The signal of the primary tumor and metastatic lymph lodes in the routine MRI began to increase at the accumulative dose of 20Gy after radiotherapy. The mean ADC value of the primary tumor and metastatic lymph nodes before radiotherapy was 0.690±0.072 X 10-3mm2/s and 0.813±0.091 X 10-3mm2/s, and kept increasing after radiotherapy, the mean ADC value at accumulative dose of 40Gy after radiotherapy was 1.167±0.057×10-3mm2/s or 1.802±0.173×10-3mm2/s, and the difference was significant(P<0.05). The mean area of the metastatic lymph nodes was 2.58±0.64 cm2 before radiotherapy, began to shrink apparently at accumulative dose of 10Gy after radiotherapy, and the reduction rate was 58.5%, but reduction rate of the primary tumor at accumulative dose of 10Gy was 2%.Conclusion1.The difference of the maximum area of the primary tumor or metastatic lymph nodes before radiotherapy was siganificant, which pointed the DW-MRI shrink the tumor outline area in some respects.2.There was no correlation between lymph nodes metastasis or the T-staging of NPC and ADCs.3.The performance of the DW-MRI was different and unsynchronized in the primary tumor or metastatic lymph nodes before radiotherapy and at different accumulative dose separately after radiotherapy, The increasing tendency of the ADCs was more early and obviously than the chang of the size in the routine MRI.