Impact of MR geometric distortion on brachytherapy in cervical cancer

Abstract

Introduction Volumetric imaging and in particular magnetic resonance (MR) has replaced the 2D imaging for brachytherapy treatment planning. However it is recognized that MR images suffer from geometric distortions which can have an impact on target and OARs DVH parameters due to high dose gradient in brachytherapy applications. Objective To assess the potential dosimetric impact of MR geometric distortion on the brachytherapy treatment planning for cervical cancer. Materials and methods MR dataset for 15 cervical cancer patients were acquired based on GEC ESTRO recommendations. Structures were delineated on the paraaxial images and treatment plans were generated using Oncentra™ TPS. In-house software was developed to calculate the deformable registration between CT and MR images of a control point based phantom and to derive a distortion map of the MR system. Geometrically corrected images were then generated by applying the inverse of the distortion map. Structures were copied and adapted to the corrected datasets and the treatment plans recomputed. Dose Volume Histograms (DVH) were evaluated for High Risk CTV (HRCTV), bladder, rectum, and sigmoid. Results Mean geometric distortions were less than 0.5 mm over a Field Of View (FOV) of 350 mm. Differences in D100 and D90 were less than 2% for HRCTV. Differences in D2cc were less than 4% for bladder, rectum, and sigmoid. Preliminary results showed that, for all organs, less than 4% of deviation was observed for D100 and D90. Conclusions For an FOV of 350 mm, MR geometric distortion has no significant dosimetric impact on DVH parameters in brachytherapy for cervical cancer. Disclosure Authors have nothing to disclose.