Evaluation of 18F-FDG PET and DWI Datasets for Predicting Therapy Response of Soft-Tissue Sarcomas Under Neoadjuvant Isolated Limb Perfusion

Our purpose was to evaluate and compare the clinical utility of simultaneously obtained quantitative ¹⁸F-FDG PET and diffusion-weighted MRI datasets for predicting the histopathologic response of soft-tissue sarcoma (STS) to neoadjuvant isolated limb perfusion (ILP). Methods: In total, 37 patients with a confirmed STS of the extremities underwent ¹⁸F-FDG PET/MRI before and after ILP with melphalan and tumor necrosis factor-α. For each patient, the maximum tumor size, metabolic activity (SUV), and diffusion restriction (apparent diffusion coefficient, ADC) were determined in pre- and posttherapeutic examinations, and percentage changes during treatment were calculated. Mann–Whitney U testing and receiver-operating-characteristic analysis were used to compare the results of the different quantitative parameters to predict the histopathologic response to therapy. Results from histopathologic analysis after tumor resection served as the reference standard, and patients were defined as responders or nonresponders based on the grading scale by Salzer-Kuntschik. Results: Histopathologic analysis categorized 22 (59%) patients as responders (grades I–III) and 15 (41%) as nonresponders (grades IV–VI). Under treatment, tumors in responders showed a mean reduction in size (−9.7%) and metabolic activity (SUV_peak, −51.9%; SUV_mean, −43.8%), as well as an increase of the ADC values (ADC_min, +29.4%; ADC_mean, +32.8%). The percentage changes in nonresponders were −6.2% in tumor size, −17.3% in SUV_peak, −13.9% in SUV_mean, +15.3% in ADC_min, and +14.6% in ADC_mean. Changes in SUV and ADC_mean significantly differed between responders and nonresponders (<0.01), whereas differences in tumor size and ADC_min did not (>0.05). The corresponding AUCs were 0.63 for tumor size, 0.87 for SUV_peak, 0.82 for SUV_mean, 0.63 for ADC_min, 0.84 for ADC_mean, and 0.89 for ratio of ADC_mean to SUV_peak. Conclusion: PET- and MRI-derived quantitative parameters (SUV and ADC_mean) and their combination performed well in predicting the histopathologic therapy response of STS to neoadjuvant ILP. Therefore, integrated PET/MRI could serve as a valuable tool for pretherapeutic assessment as well as monitoring of neoadjuvant treatment strategies of STS.