Abstract: Objective To investigate the value of diffusion-weighted imaging (DWI) for evaluating short-term efficacy of cyber knife in the treatment of small hepatocellular carcinoma.Methods Twenty-three patients (24 lesions) diagnosed with small hepatocellular carcinoma in our hospital from February 2017 to December 2017 were enrolled. All the 23 patients underwent non-enhanced magnetic resonance imaging (MRI) scans and DWI scans of the liver before cyber knife, 1 month, 3 months and 6-12 months after cyber knife; as well as dynamic contrast-enhanced MRI scans of the liver before treatment, 3 months and 6-12 months after treatment. According to the modified response evaluation criteria in solid tumors, the complete necrosis and residual activity of tumor 6-12 months after cyber knife were assessed. The apparent diffusion coefficient (ADC) values of residual active tissue, necrosis in tumor and normal liver tissue at different times were measured. Paired t test was used to compare ADC values of tumor necrosis lesions and normal liver tissues before and after treatment, and receiver operating characteristic (ROC) curve was used to evaluate the efficacy of ADC values in predicting complete tumor necrosis after treatment. Results Among the 24 lesions, 23 lesions were completely necrotic, and active tissues were found in 1 lesion after treatment. The ADC values of the completely necrotic tumor tissues 1 month and 3 months after treatment were higher than that before treatment, with statistical difference (P<0.05). There were no statistically significant differences in ADC of normal liver tissue 1 month or 3 months after treatment compared with that before treatment (P>0.05). The area under the ROC curve of ADC value for predicting the complete necrosis in tumor tissues after cyber knife was 0.830. And the cut-off value of ADC was 1.29×10^-3 mm²/s, with sensitivity of 85.7% and specificity of 47.6%.Conclusion The ADC value helps to distinguish the necrotic component from the active component of small hepatocellular carcinoma 1 month after cyber knife, and can be used to evaluate the short-term efficacy of cyber knife in small hepatocellular carcinoma.

Key words: Small hepatocellular carcinoma, Magnetic resonance imaging, Cyber knife