Synopsis

Neoadjuvant chemotherapy has been widely applied in treating locally advanced rectal cancer (LARC) for effectively decreasing the local recurrence after total mesorectal excision(TME). The imaging technique of intravoxel incoherent motion(IVIM) model could estimate tissue perfusion and diffusion components individually using multi-b-values^1-3. Here, we try to investigate the value of intravoxel incoherent motion (IVIM) derived parameters in predicting pathological complete regression (pCR) in patients with LARC during mid-term of neoadjuvant chemoradiotherapy (CRT) before completing chemotherapy. We found that Pre-CRT ADC, D and their corresponding percentage changes during the mid-term of CRT were quite useful for discrimination between pCR and non-pCR patients.

Purpose

To investigate the value of intravoxel incoherent motion (IVIM) derived parameters in predicting pathological complete regression (pCR) in patients with locally advanced rectal cancer during mid-term of neoadjuvant chemoradiotherapy (CRT).

Methods

Totally, 41 patients (31 men, 10 women; mean age, 58.34±10.02 years; age range, 35-76 years) with rectal cancers underwent pelvis magnetic resonance imaging (MRI) examination before and during CRT. The first pelvic MRI was performed within one week before CRT, and the mid-term MRI was 40 days after CRT (range, 30~45days). All pelvis examinations were performed in 3.0T MR unit including high spatial resolution T2-weighted imaging (HR-T2WI) and diffusion-weighted imaging (DWI) sequences. Totally, 16 b values (0, 10, 20, 30, 40, 60, 80, 100, 150, 200, 400, 800, 1000,1200, 1500, and 2000 s/mm2) were set in DWI sequence. The apparent diffusion coefficient (ADC) and IVIM parameters (D, pure diffusion; f, perfusion fraction; D*, pseudo-diffusion coefficient) were calculated independently by two radiologists. Regions of interest (ROIs) were manually drawn to contour the border the tumor on each slice (pre-CRT and mid-term of CRT DWI images) with the corresponding HR-T2 weighted images available as anatomic reference. The parameters and their corresponding percentage changes (ΔADC%, ΔD%, Δf%, ΔD*%) were compared between pCR and non-pCR using independent samples t test or Mann-Whitney U test. Receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic performance of DWI derived parameters in predicting pCR. The area under the ROC curve (AUC) and the optimal cut-off values were calculated, meanwhile sensitivity, and specificity were determined. Intra- and inter-observer agreement of ADC and IVIM parameters were evaluated using the intraclass correlation coefficient (ICC). P＜0.05 was considered to indicate a statistically significant difference.

Results

There were 12 pCR patients and 29 non-pCR patients. Relatively good to excellent intra- and inter-observer agreement was observed for DWI derived parameters measurement ( intra-observer, 0.7939~0.9863; inter-observer, 0.7550~0.9836 ). Lower Pre-CRT ADC, Pre-CRT D , larger ΔADC% and ΔD% values were showed in pCR group than those in non-pCR group (p=0.039, p=0.001, p=0.036, p=0.001, respectively) (Figure 1,2). However, no significant statistical differences were found in Mid-term DWI derived parameters between the aforementioned two groups. According to ROC curve, pre-CRT ADC, pre-CRT D, ΔADC% and ΔD% values showed diagnostic significance with the AUC values of 0.697, 0.836, 0.710, 0.822, respectively. The optimal cutoff value was 0.97×10-3mm2/s for pre-CRT ADC, 0.63×10-3mm2/s for pre-CRT D, 22.47% for ΔADC%, 11.19% for ΔD% (Figure 3,4).

Conclusion

Pre-CRT ADC, D and their corresponding percentage changes during the mid-term of CRT were quite useful for discrimination between pCR and non-pCR patients. IVIM parameter-D may be used as a promising parameters to evaluate pathological complete regression to CRT in rectal cancer during the mid-term of CRT.

Acknowledgements

No acknowledgement found.