[ 15 O]H 2 O PET/MRI for Assessment of Complete Response to Neoadjuvant or Induction Chemotherapy in Patients with Muscle-Invasive Bladder Cancer: A Pilot Study.

Background: Accurate assessment of therapy response to chemotherapy could possibly offer a bladder-sparing approach in selected patients with localized muscle-invasive bladder cancer (MIBC). The aim of this study was to evaluate whether [ 15 O]H 2 O PET/MRI can be used for assessment of complete local pathological response to preoperative chemotherapy in patients with MIBC. Methods: This prospective pilot study included 13 patients with MIBC treated with neoadjuvant or induction chemotherapy and subsequent radical cystectomy. Patients underwent a [ 15 O]H 2 O PET/MRI scan before chemotherapy and another scan after chemotherapy before radical cystectomy. Volumes of interest were delineated on T2-weighted MRI and transferred to parametric images for dynamic analysis. Tumor blood flow (TBF) was estimated by [ 15 O]H 2 O PET. Changes in TBF were compared with histopathology. The Wilcoxon matched-pairs signed-ranks test was used for comparing pre- and post-chemotherapy measurements. Results: Mean TBF decreased by 49%. Mean TBF in complete responders (ypT0N0/ypTis) was not significantly different from non-complete responders (≥ypT1) ( p = 0.52). Conclusions: Despite a measurable decrease in TBF after chemotherapy treatment, we were not able to estimate a TBF threshold for identifying complete responders to chemotherapy for MIBC patients. Further studies are needed to elucidate the potential of [ 15 O]H 2 O PET/MRI in assessing therapy response in MIBC.