Longitudinal Assessment of Intravoxel Incoherent Motion Diffusion Weighted Imaging in Evaluating the Radio-sensitivity of Nasopharyngeal Carcinoma Treated with Intensity-Modulated Radiation Therapy

PURPOSE: Intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI)was evaluated regarding its ability to preliminarily predict the short-term treatment response of nasopharyngeal carcinoma (NPC) following intensity-modulated radiation therapy. MATERIALS AND METHODS: IVIM-DWI with 14 b-factors (0-1,000 sec/mm(2)) was performed with a 3T MR system on 47 consecutive NPCs before, during (end of the 5th, 10th, 15th, 20th, and 25th fractions), and after fractional radiotherapy. IVIM parametrics (D, f, and D*) were calculated and compared to the baseline and xth fraction. Patients were categorized into responders and non-responders after radiotherapy. IVIM parametrics were also compared between subgroups. RESULTS: After fractional radiations, the D (except D(5) and D at the end of the 5th fraction) after radiations were larger than the baseline D(0) (p < 0.05), and the post-radiation D* (except D*(5) and D*10) were smaller than D*(0) (p < 0.05). f(0) was smaller than f(5) and f(10) (p < 0.001) but larger than f(end) (p < 0.05). Furthermore, greater D(5), D(10), D(15), and f(10) coupled with smaller f(0), D*(20), and D*(25) were observed in responders than non-responders (all p < 0.01). Responders also presented larger ΔD(10), Δf(10), ΔD*(20), and δD*(20) than non-responders (p < 0.05). Receiver operating characteristic curve analysis indicated that the D(5), D*(20), and f(10) could better differentiate responders from non-responders. CONCLUSION: IVIM-DWI could efficiently assess tumor treatment response to fractional radiotherapy and predict the radio-sensitivity for NPCs.