Soft tissue sarcoma DCE-MRI data collected at baseline and after one chemotherapy cycle were shared among nine centers and individual arterial input functions (AIFs) were quantified with center-specific methods. Pharmacokinetic (PK) modeling of the data was performed with these AIFs and the Tofts model. Considerable variations in estimated PK parameters and the corresponding percent changes were observed due to AIF variations. kep is less susceptible to AIF variation than Ktrans and may be a more robust imaging biomarker of microvasculature. kep percent change correlates in a uniformly negative relationship with necrosis percentage of resection specimen across all individually measured AIFs.