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Evaluating Radiation-Induced Changes with Diffusion Weighted MRI and Dynamic Contrast Enhanced MRI in Patients with Early Stage Breast Cancer Treated with Stereotactic Body Radiotherapy: Initial Results

Z Chang*, F Yin, S Yoo, J Horton, Duke University Medical Center, Durham, NC

SU-E-CAMPUS-J-4 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Pre-operative stereotactic body radiosurgery (SBRT) was delivered in a single fraction to treat patients with early stage breast cancer; however, few data are available regarding radiation-induced changes by SBRT. In this work, diffusion weighted imaging (DWI) and dynamic contrast enhanced (DCE) MRI were used to assess the radiation-induced changes following SBRT.

Methods:
In this study, 24 patients with early stage breast cancer were enrolled. A prescription dose of 15, 18 or 21Gy was delivered in a single fraction using intensity-modulated radiotherapy. Patients were to be scanned with MRI about 1-week before and 1-week after SBRT. Among the patients, 13 patients have both pre-and post-MRI scans, and are analyzed in the work. The 13 patients include 6 patients receivng 15Gy, 3 patients receiving 18 Gy and 4 patients receiving 21Gy.

DWI and DCE-MRI scans were acquired on a 1.5T GE clinical scanner using a standard 4-channel breast coil. Apprant diffusion coefficient (ADC) and initial area under the concentration-time curve for 5-min after injection (iAUC5min) was used to assess radiation-induced changes. Descriptive statistics of regional ADC (rADC) and regional iAUC5min was obtained for Gross Tumor Volume (GTV). Wilcoxon signed-rank test was used to assess the changes, with statistical significance considered at p < 0.05.

Results:
After delivery of SBRT, the mean rADC increased from the baseline value by about 17% (p=0.030). Similarly, the mean iAUC5min increased from 1.93+/-0.20 mM-min to 2.31+/-0.16 mM-min, about 16% (p= 0.012) after treatment.

Conclusion:
In this study, MRI data revealed significant increases in rADC and iAUC of GTV after SBRT. The radiation-induced changes after SBRT might imply microscopic water diffusion and microvascular change with an ablative radiotherapy dose. Further work is required to investigate the dose related changes and to determine whether the differences in baseline and individual treatment-related changes have prognostic value.

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