Purpose: To develop a multi-parametric quantitative MR protocol for pre-operative radiotherapy response assessment in Soft-Tissue Sarcomas (STS).
Methods: A multi-parametric MR protocol including diffusion-weighted imaging (DWI), magnetization-transfer imaging (MT) and multi-echo echo-planar imaging (EPI) was developed. The DWI and multi-echo EPI were pixel-matched, and the MT imaging was matched as closely as possible to the DWI/EPI Field-of-View (FoV) and pixel spacing. All had the same central imaging slice and slice thickness (5.0mm). Seven patients with limb STS were imaged at baseline (B0) and following radiotherapy treatment (postRT). Regions of interest were drawn around the tumour and the mean values of the apparent diffusion coefficient (ADC), T2 value and magnetization-transfer ratio (MTR) extracted. Paired t-tests were run for the B0 and postRT values for each metric. The difference between B0 and postRT values was calculated. The Pearsons correlation coefficient between the difference values for (MT, ADC), (MT, T2) and (ADC, T2) was calculated.
Results: Negative correlations were observed between the change in MTR & ADC values following radiotherapy (r=-0.635, p=0.125) and for the change in MTR & T2 values (r=-0.609, p=0.147). No correlation was observed between the change in ADC & T2 values (r=-0.0135, p=0.977). For most patients the ADC value increased while the MTR decreased. Some tumours exhibited changes in the opposite direction. The T2 change was mixed. There were no significant changes observed in the individual metrics before and after radiotherapy.
Conclusion: Preliminary results demonstrate that patients with STS show change in a range of quantitative metrics (ADC, MTR and T2) following radiotherapy and these metrics capture heterogeneous changes, typical of these tumours. This encourages further investigation into these metrics as response markers. Further work will explore these metrics in a larger cohort of patients and explore additional metrics including T1 and enhancing fraction.
Funding Support, Disclosures, and Conflict of Interest: David & Ruth Lewis Family Charitable Trust, Sarcoma UK grant SUK105.2018
Quantitative Imaging, MRI, Radiation Therapy