Discussion of the diffusion weighted imaging on predicting therapeutic effect of radiotherapy treatment in nasopharyngeal carcinoma

Objective: To discuss the application value of DWI and ADC on predicting therapeutic effect of radiotherapy treatment in NPC. Methods: Twenty four local recurrent cases and 38 non-recurrent cases after radiotherapy treatment in NPC were reviewed. MRI and DWI-MRI were performed at pre-radiotherapy and 3, 6, 12 months after treatment, the ADC values of the lesions were analyzed by SPSS 18.0 statistical software. ROC curves based on the ADC values were measured in 3, 6, 12 months after treatment plotted to analyze the threshold ADC value for confirming recurrence. Results: The recurrent group and newly diagnosed group showed significantly high signal on DWI, while the non-recurrent group acquired low or mixed signal. The ADC values of the primary tumor in the recurrent group and the non-recurrent group were (0.709 ± 0.078) × 10^-3 and (0.693 ± 0.089) × 10^-3 mm²/s, respectively, t = -0.717, P > 0.05, respectively. The ADC values of the primary and recurrent tumor in the recurrent group were (0.730 ± 0.068) × 10^-3 mm²/s and (0.709 ± 0.078) × 10^-3 mm²/s, t = -1.000, P > 0.05, respectively. There were statistical differences between the recurrent group and the non-recurrent group for ADC in 3, 6, 12 months after treatment:(1.128 ± 0.179) × 10^-3 and (1.358 ± 0.145) × 10^-3 mm²/s, t = 5.567, P < 0.01; (1.164 ± 0.174) and (1.450 ± 0.102) × 10^-3 mm²/s, t = 7.310, P < 0.01;(1.107 ± 0.180) × 10^-3 and (1.584 ± 0.125) × 10^-3 mm²/s, t= 11.189, P < 0.01; respectively. Take 1.29 × 10^-3 mm²/s, 1.32 × 10^-3 mm²/s, 1.37 × 10^-3 mm²/s respectively in 3, 6, 12 months after treatment as the diagnostic threshold to predict tumor recurrence. The sensitive, specificity, and accuracy were (83.3%, 73.7%, 77.4%), (83.3%, 89.5%, 87.1%), (100.0%, 94.7%, 96.3%). Conclusions: Both DWI and ADC value are important for diagnosing and predicting recurrent NPC after radiotherapy treatment, DWI and ADC can be used to regular follow-up after radiotherapy, to further improve the rate of early diagnosis of recurrent NPC. (authors)