Baseline and early response 2-[18F]FDG-PET/MRI for prediction of radiotherapy outcome in uterine cervical squamous cell carcinoma: a prospective single-center observational cohort study

Should early response imaging predict tumor response to therapy, personalized treatment adaptations could be feasible to improve outcome or reduce the risk of adverse events. This prospective single-center observational study on 2-fluorine-18-fluoro-deoxy-glucose (2-[18F]FDG) positron-emission tomography/magnetic resonance imaging (PET/MRI) features aims to investigate the association between semantic 2-[18F]FDG-PET/MRI imaging parameters and outcome prediction in uterine cervical squamous cell carcinoma (CSCC) treated with radiotherapy. Eleven study participants with previously untreated CSCC were examined with 2-[18F]FDG-PET/MRI at baseline and approximately one week after start of curative radiotherapy. All study participants had at least 24 months clinical follow-up. Two patients relapsed during the follow-up period. Reduced tumor size according to visual assessment was present in 9/11 participants (median change in sum of largest diameters (SLD) − 10.4%; range − 2.5 to − 24.6%). The size reduction was less pronounced in the relapse group compared to the no relapse group, with median change in SLD − 4.9%, versus − 10.4%. None of the reductions qualified as significantly reduced or increased in size according to RECIST 1.1., hence all participants were at this stage classified as non-responders/stable disease. Median baseline functional tumor volume (FTV) for the relapse group was 126 cm3, while for the no relapse group 9.3 cm3. Median delta FTV in the relapse group was 50.7 cm3, representing an actual increase in metabolically active volume, while median delta FTV in the no relapse group was − 2.0 cm3. Median delta apparent diffusion coefficient (ADC) was lower in the relapse group versus the no relapse group (− 3.5 mm2/s vs. 71 mm2/s). Early response assessment with 2-[18F]FDG-PET/MRI identified potentially predictive functional imaging biomarkers for prediction of radiotherapy outcome in CSCC, that could not be recognized with tumor measurements according to RECIST 1.1. These biomarkers (delta FTV and delta ADC) should be further evaluated. Trial registration Clinical Trials, NCT02379039. Registered 4 March 2015—Retrospectively registered, https://classic.clinicaltrials.gov/ct2/show/study/NCT02379039 .