Room: AAPM ePoster Library
Purpose: To investigate the feasibility of using Diffusion Weighted Imaging (DWI) to identify patterns in diffusion changes within brain metastases before and after stereotactic radiosurgery (SRS) treatment.
Methods: DWI Magnetic Resonance Images (MRI) were acquired as part of a routine SRS pre-treatment protocol. Apparent Diffusion Coefficient (ADC) maps were calculated using manufacturer provided calculation models with b-values of 0 and 1000 s/mm². Computed tomography and MRI images were fused to ADC maps. Metastases contoured by the Radiation Oncologist were used to examine ADC changes before and after treatment. Histograms of ADC values within each metastasis were calculated in MIM Maestro (MIM Software Inc.) over multiple pre and post DWI MRI scans. Major peaks were analyzed, and kurtosis and skewness of the histograms were evaluated.
Results: Six patients with a total of 52 metastases were included in this study. Results showed that metastases can be divided into three patterns based on their ADC histograms. In 42% of analyzed metastases, distributions were observed to show increasingly restricted diffusion and greater homogeneity during metastases formation leading up to the treatment. Following SRS treatment, distributions of ADC voxels flatten (lower kurtosis) and move towards greater heterogeneity and diffusion. In 23% of metastases distributions showed the same restricted diffusion pattern but stayed homogeneous before and after SRS treatment. In the remaining 35% of metastases, ADC distributions showed either random or no change.
Conclusion: In this feasibility study we developed a method of ADC map analysis for patients with brain metastases. Our preliminary results identified several patterns of ADC change before and after the treatment. We built a framework to correlate these changes with clinical parameters for potential use in forming predictive models, aiding prognoses, and tracking treatment response.