18-Fluoro-Deoxy-Glucose Positron Emission Tomography With Computed Tomography-Based Gross Tumor Volume Estimation and Validation With Magnetic Resonance Imaging for Locally Advanced Cervical Cancers

Purpose: Anatomy and morphology-based imaging is routinely used for radiotherapy purpose to deliver precision treatment. There is an interest in using information from functional imaging for conformal radiation therapy planning. These functional imaging techniques need to be validated rigorously before their routine use. We attempted to evaluate and validate the use of 18-fluoro-deoxy-glucose positron emission tomography with computed tomography ((18)FDG PET-CT) on primary tumor of the cervical carcinoma, with an aim of arriving at a cutoff maximum standardized uptake value (SUVmax) at which the tumor volume correlates best with magnetic resonance imaging (MRI). This observational study was a part of an ethics committee-approved study evaluating pretreatment MRI and FDG PET-CT. Materials and Methods: Patients' biopsy-proven cervical carcinomas (stages IIB and IIIB) were included in this study and underwent pretreatment MRI and FDG PET-CT as per institutional protocol. Volumes of the disease at the cervix on the MR image were calculated. Volumes at the FDG PET-CT scan at different percentages of SUVmax were auto contoured. Volume at MRI was correlated with each different percentage cutoff of the SUVmax. Results: Data of 74 patients were available for the study. The mean (SD) SUVmax of the primary tumor was 15.7 (7.0). The mean MRI volume correlates significantly (P < 0.001) with 30% and 35% of SUVmax values with good correlation according to the Pearson bivariate correlation (r = 0.79 each). The mean difference between MRI and PET volumes was least with 30% SUVmax. Conclusions: (18)FDG PET-CT SUV-based primary tumor volume estimation at 30% to 35% of SUVmax values correlates significantly with the criterion standard MR volumes for primary cervical tumor with squamous histology in our population.