Synopsis

Neoadjuvant chemoradiation therapy (CRT) followed by surgery has been established as the standard for locally advanced rectal cancer¹. The treatment response after CRT is normally evaluated by MRI. However, MRI morphology techniques suffer from limitations in the interpretation of fibrotic scar tissue and inflammation. Diffusion kurtosis imaging (DKI) is an emerging technique, which could reflect restricted water diffusion within the complex microstructure of most tissues based on non-Gaussian diffusion model². There is limited research reported about the clinical application of DKI in rectal cancer, and the value of DKI in monitoring rectal cancer treatment was still mysterious.

Purpose

To determine the diagnostic performance of diffusion kurtosis imaging (DKI) in the assessment of complete regression to chemoradiation therapy (CRT) in patients with locally advanced rectal cancers, with tumor regression grade (TRG) obtained by postoperative pathological results as the reference standard.

Methods

Totally, 68 patients (53 men, 15 women; mean age, 58.76±10.85 years; age range, 26-77 years) who underwent pre- and post-CRT pelvis magnetic resonance imaging (MRI) examination followed by surgery were enrolled in the study. All pelvis MRI examinations were performed in 3.0T MR unit (Philips 3.0T Ingenia, Philips Medical System, The Netherlands) including high spatial resolution T2-weighted imaging (HR-T2WI) and diffusion-weighted imaging (DWI) sequences. DWI sets with the corresponding HR-T2WI available for anatomic reference. Totally, seven b values (0, 400, 800 1000, 1200, 1500 and 2000s/mm2) were adopted and DKI derived parameters (MD, mean diffusivity; MK, mean kurtosis; FA, fractional anisotropy) were measured independently by two radiologists using IDL 6.3 software (ITT Visual Information Solutions, Boulder, CO, USA). According to final histopathologic results, patients were divided into two groups: complete regression (CR) group (TRG1) and non-CR group (TRG 2-5). The pre- and post-CRT DKI parameters between CR and non-CR measured were compared by using independent samples t test or Kolmogorov-Smirnov test, and relevant diagnostic performance in the prediction of the response to CRT was evaluated by receiver operating characteristic (ROC) analysis. In addition, the corresponding difference values between pre- and post-CRT DKI parameters were also calculated and compared in different CRT response groups(ΔDKI parameters’ value=DKI parameters’ value_post - DKI parameters’ value_pre). The area under the ROC curve (AUC) and the optimal cut-off values were calculated, meanwhile sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined. Interobserver agreement of DKI derived parameter were evaluated using the intraclass correlation coefficient (ICC). P＜0.05 was considered to indicate a statistically significant difference.

Results

The two readers showed excellent interobserver agreement (ICC=0.8988-0.9499; narrow with of 95% limits of agreement). 9 patients showed complete regression to CRT and non-CR was noted in 59 patients. MDpre values were significantly lower in CR group than in non-CR group (p=0.032), while MKpre and FApre values showed different trend (CR group: MK =0.97±0.20, FA=0.17±0.03; non-responders: MK =0.88±0.17, FA=0.12±0.07) (Table 1). No differences in MDpost and MKpost values were observed between CR and non-CR groups, while FApost values showed significantly higher values in CR group (p=0.001). DMD demonstrated statistical difference between CR and non-CR groups(p=0.046), however, no similar trend was found in ΔMK and ΔFA values. According to ROC curve, the AUC values for MDpre, FApre, FApost, DMD were 0.755, 0.792, 0.794, 0.808, respectively. The optimal cutoff value was 1.087×10-3mm2/s for MDpre (MDpre values of CR patients were lower than this value; sensitivity 83.05%, specificity 77.78%, PPV 96.07%, NPV 41.18% ), 0.140 for FApre (FApre values of CR patients was greater than this value; sensitivity 88.89%, specificity 69.49%, PPV 30.77%, NPV 97.62% ), 0.148 for FApost (FApost values of CR patients was greater than this value; sensitivity 71.43%, specificity 78.05%, PPV 35.71%, NPV 94.12% ), and -0.078 for DMD (DMD values of CR patients was lower than this value; sensitivity 100%, specificity 68.29%, PPV 35.00%, NPV 100% ).

Conclusion

DKI derived parameters were promising non-invasive index to evaluate tumor complete regression to CRT in locally advanced rectal cancer and further studies with larger sample size are needed to confirm this results.

Acknowledgements

No acknowledgement found.