Assessment of early treatment response to neoadjuvant chemotherapy in breast cancer using non-mono-exponential diffusion models: a feasibility study comparing the baseline and mid-treatment MRI examinations.

Abstract

$\textit{Objectives}$: To assess the feasibility of the mono-exponential, bi-exponential and stretched-exponential models in evaluating response of breast tumours to neoadjuvant chemotherapy (NACT) at 3 T. $\textit{Methods}$: Thirty-six female patients (median age 53, range 32-75 years) with invasive breast cancer undergoing NACT were enrolled for diffusion-weighted MRI (DW-MRI) prior to the start of treatment. For assessment of early response, changes in parameters were evaluated on mid-treatment MRI in 22 patients. DW-MRI was performed using eight $b$ values (0, 30, 60, 90, 120, 300, 600, 900 s/mm$^2$). Apparent diffusion coefficient (ADC), tissue diffusion coefficient ($D_t$), vascular fraction (ƒ), distributed diffusion coefficient (DDC) and alpha ($\alpha$) parameters were derived. Then $t$ tests compared the baseline and changes in parameters between response groups. Repeatability was assessed at inter- and intraobserver levels. $\textit{Results}$: All patients underwent baseline MRI whereas 22 lesions were available at mid-treatment. At pretreatment, mean diffusion coefficients demonstrated significant differences between groups ($p$ < 0.05). At mid-treatment, percentage increase in ADC and DDC showed significant differences between responders (49 % and 43 %) and non-responders (21 % and 32 %) ($p$ = 0.03, $p$ = 0.04). Overall, stretched-exponential parameters showed excellent repeatability. $\textit{Conclusion}$: DW-MRI is sensitive to baseline and early treatment changes in breast cancer using non-mono-exponential models, and the stretched-exponential model can potentially monitor such changes.The study has received funding from the Addenbrookes Charitable Trust and the NIHR comprehensive Biomedical Research Centre (BRC) and the Experimental Cancer Medicine Centre (ECMC) awards to Cambridge University Hospitals NHS Foundation Trust in partnership with the University of Cambridge