Use of Baseline 18F-FDG PET/CT to Identify Initial Sub-Volumes Associated With Local Failure After Concomitant Chemoradiotherapy in Locally Advanced Cervical Cancer

Introduction: Locally advanced cervical cancer (CC) patients treated by chemoradiotherapy (CRT) have a significant local recurrence rate. The purpose of this study was to evaluate the overlap between the initial high-uptake sub-volume (V1) on baseline 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) scans and the metabolic relapse (V2) sites after CRT in locally advanced CC. Methods: PET/CT performed before treatment and at relapse in 21 patients diagnosed with LACC and treated with CRT were retrospectively analyzed. CT images at the time of recurrence were registered to baseline CT using the 3D Slicer TM Expert Automated Registration module. The corresponding PET images were then registered using the corresponding transform. The fuzzy locally adaptive Bayesian (FLAB) algorithm was applied using 3 classes (one for the background and the other two for tumour) in PET1 to simultaneously define an overall tumour volume and the sub-volume V1. In PET2, FLAB was applied using 2 classes (one for background, one for tumour), in order to define V2. Four indices were used to determine the overlap between V1 and V2 (Dice coefficients, overlap fraction, X= (V1∩V2)/V1 and Y= (V1∩V2)/V2). Results: The mean (±standard deviation) follow-up was 26±11 months. The measured overlaps between V1 and V2 were moderate to good according to the four metrics, with 0.62 to 0.81 (0.72±0.05), 0.72 to 1.00 (0.85±0.10), 0.55 to 1.00 (0.73±0.16) and 0.50 to 1.00 (0.76±0.12) for Dice, overlap fraction, X and Y, respectively. Conclusion: In our study, the overlaps between the initial high-uptake sub-volume and the recurrent metabolic volume showed moderate to good concordance. These results now need to be investigated in a larger cohort using a more standardized patient repositioning protocol for sequential PET/CT imaging, as there is potential for RT dose escalation exploiting the pre-treatment PET high-uptake sub-volume.