ESTRO 2021 Abstract Book

S342

ESTRO 2021

University Hospital, The Norwegian Hospital, Department of Radiation Biology, Oslo, Norway

Purpose or Objective Patients with locally advanced cervical cancer (LACC) are treated with definitive chemoradiotherapy. A significant number of patients experiences treatment failure, and an improved pretreatment risk stratification is warranted. Tumor hypoxia and high glycolytic activity are aggressive features assessable from diagnostic MR and FDG-PET images, respectively. In this study we aimed to investigate the prognostic potential of imaging biomarkers with respect to these features. Materials and Methods A total of 82 prospectively collected LACC patients, all examined with multiparametric MRI and FDG-PET as part of standard diagnostic work-up, were included. A separate cohort of 38 patients with MRI, but no FDG- PET, was included for validation of the MRI results. The primary tumor was contoured manually on all imaging modalities. The prognostic value of Ktrans, apparent diffusion coefficient (ADC) and standardized uptake volume SUV peak extracted from contrast-enhanced MRI (DCE-MRI), diffusion-weighted MRI (DW-MRI) and FDG- PET respectively, were calculated. ADC and Ktrans were used as surrogate markers for oxygen consumption and supply, and were voxel-wise combined into hypoxia images by a previously reported method. The optimal cut-off between hypoxic and non-hypoxic pixels with respect to outcome was determined, and the tumor hypoxic fraction (tHF) was calculated. The clinical endpoint was disease free survival (DFS). Cox proportional hazards regression was used for modelling of DFS. Kaplan-Meier curves were compared by log-rank test. Correlations between variables were assessed using the Spearman correlation test. Results No or only weak correlation was found between Ktrans, ADC and SUV peak indicating that the images provide different information about tumor phenotype. Low Ktrans was significantly associated with a poor DFS (p= 0.004), whereas associations were found for low ADC (p=0.065) and high SUV peak (p=0.071). The tHF showed a stronger association with DFS than Ktrans alone, and patients with a high tHF had a significantly shorter DFS (p<0.0001, Figure 1). The MRI findings were confirmed in the validation cohort (tHF p=0.014 (Figure 2)and Ktrans p=0.086). A significant positive correlation was found between tHF and SUV peak (Spearman R=0.34 and p=0.002).

Conclusion In this study MRI was superior to FDG-PET for the identification of LACC patients at risk of recurrence. Our study provides a non-invasive method for hypoxia assessment based on the combined information from DW- and DCE-MRI, which improves the prognostic impact compared to Ktrans and ADC alone. Hypoxic tumors tended to have a higher glycolytic activity than non-hypoxic tumors. Our approach relies on standard diagnostic images, which facilitates clinical implementation. PH-0443 The role of 18FDG-PET/CT target volume delineation in locally advanced cervical cancer radiotherapy L. Vicenzi 1 , S. Costantini 2 , C. Di Carlo 1 , F. Cucciarelli 1 , C. Mariucci 1 , A. Palucci 3 , L. Burroni 3 , M. Valenti 4 , G. Mantello 1 1 Azienda Ospedaliero Universitaria Ospedali Riuniti, Radiotherapy, Ancona, Italy; 2 Azienda Ospedaliero Universitaria Ospedali Riuniti, Radiotherapy , Ancona, Italy; 3 Azienda Ospedaliero Universitaria Ospedali Riuniti, Nuclear Medicine, Ancona, Italy; 4 Azienda Ospedaliero Universitaria Ospedali Riuniti, Medical Physics, Ancona, Italy Purpose or Objective To evaluate the impact of 18 FDG-PET/CT in optimizing radiotherapy dose and volume prescription in patients (pts) affected by locally advanced cervical cancer with involved lymph nodes on imaging. Materials and Methods Between December 2015 and April 2020, 43 pts with locally advanced cervical cancer were retrospectively analyzed. Patients underwent definitive Intensity Modulated Radiotherapy on pelvis +/- para-aortic region and concurrent weekly platinum-based chemotherapy. Subsequently, interventional radiotherapy (brachytherapy) was applied when feasible. All pts carried out planning 18 FDG-PET/CT. CT was performed in 35 patients and