Evaluation of Monoexponential, Stretched-Exponential and Intravoxel Incoherent Motion MRI Diffusion Models in Early Response Monitoring to Neoadjuvant Chemotherapy in Patients With Breast Cancer-A Preliminary Study

Background There has been a growing interest in exploring the applications of stretched-exponential (SEM) and intravoxel incoherent motion (IVIM) models of diffusion-weighted imaging (DWI) in breast imaging, with the focus on differentiation of breast lesions. However, the use of SEM and IVIM models to predict early response to neoadjuvant chemotherapy (NACT) has received less attention. Purpose To investigate the value of monoexponential, SEM, and IVIM models to predict early response to NACT in patients with primary breast cancer. Study Type Prospective. Population Thirty-seven patients with primary breast cancer (aged 46 +/- 11 years) due to undergo NACT. Field Strength/Sequences A 1.5-T MR scanner, T-1-weighted three-dimensional spoiled gradient-echo, two-dimensional single-shot spin-echo echo-planar imaging sequence (DWI) at six b-values (0-800 s mm(-2)). Assessment Tumor volume, apparent diffusion coefficient, tissue diffusion (D-t), pseudo-diffusion coefficient (D-p), perfusion fraction (f), distributed diffusion coefficient, and alpha (alpha) were extracted, following volumetric sampling of the tumors, at three time-points: pretreatment, post one and three cycles of NACT. Statistical Tests Mann-Whitney test, receiver operating characteristic (ROC) curve. Statistical significance level was P < 0.05. Results Following NACT, 17 patients were determined to be pathological responders and 20 nonresponders. Tumor volume was significantly larger in nonresponders at each MRI time-point and demonstrated reasonable performance in predicting response (area under the ROC curve [AUC] = 0.83-0.87). No significant differences between groups were found in the diffusion coefficients at each time-point (P = 0.09-1). The parameters alpha (SEM), f, and f x D-p (IVIM) were able to differentiate between response groups after one cycle of NACT (AUC = 0.73, 0.72, and 0.74, respectively). Conclusion Diffusion coefficients derived from the monoexponential, SEM, and IVIM models did not predict pathological response. However, the IVIM-derived parameters f and f x D-p and the SEM-derived parameter alpha were able to predict response to NACT in breast cancer patients following one cycle of NACT. Level of Evidence 2 Technical Efficacy Stage 2

Automated summary

This study aimed to investigate the value of diffusion coefficients derived from different models in predicting early response to neoadjuvant chemotherapy in patients with primary breast cancer. The results showed that tumor volume had reasonable performance in predicting response, while diffusion coefficients derived from the monoexponential, stretched-exponential, and intravoxel incoherent motion models did not accurately predict pathological response. However, certain derived parameters (such as alpha from the stretched-exponential model, and f and f x D-p from the intravoxel incoherent motion model) were able to predict the degree of response in breast cancer patients after one cycle of neoadjuvant chemotherapy.