Comparison of computed tomography with magnetic resonance imaging for imaging-based clinical target volume contours in cervical cancer brachytherapy

PURPOSE: To compare CT- and MRI-based brachytherapy (BT) target volumes for patients with advanced cervical cancer so as to identify those who benefit most from MRI-based planning. We also studied how the natural mobility of the organ at risks (OARs) affects the given doses. METHODS AND MATERIALS: Subjects were 60 patients with International Federation of Gynecology and Obstetrics (FIGO) Stage IB-IVA cervical cancer. The CT high-risk clinical target volume (HR-CTV) was first delineated, then the MRI HR-CTV, with volume discrepancies calculated by subtraction. The DICE coefficient (DC) of similarity was calculated from a superimposition of the volumes. Maximum doses delivered to D-2ce of OARs in CT and MRI plans were compared; the effect of time on the natural mobility was analyzed. RESULTS: The mean HR-CTVs and the maximum doses given to OARs in CT- and MRI-based planes were similar. Multivariate analysis showed that deep infiltration affecting the uterine corpus and bowel loops adjacent to the cervix were the factors significantly impacting on the volume discrepancy between CT and MRI HR-CTV (p = 0.001, p = 0.045) and on the DC (p = 0.005, p = 0.028). Univariate analysis demonstrated that the FIGO stage had a significant impact on DC (p = 0.022). Patients with bowel loops adjacent to the cervix had lower body mass indices (p = 0.003). The median difference between the doses given in CT- and MRI-based plans, caused by mobility, were 0.5 Gy, 0.3 Gy, and 0.45 Gy per fraction for the rectum, bladder and sigmoid, respectively. No correlation of observed uncertainties and time between image acquisitions was detected. CONCLUSIONS: CT- or MRI-based scans at BT are adequate for OAR dose-volume histograms analysis. Cervical cancer patients with deep infiltration affecting the uterine corpus, a low body mass index with bowel loops adjacent to the cervix and an FIGO Stage III-IVA benefit most from MRI-based planning of BT. (C) 2018 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.