Diffusion weighted MRI (DWI) for brachytherapy in locally advanced cervical cancer - Determining the degree of distortion at 1.5T and 3T MRI

Abstract

Diffusion Weighted MRI (DWI) enables identification of tissue with high cellular density such as tumors. This makes DWI a potentially valuable tool in oncology imaging for both diagnostic imaging and monitoring of treatment. Locally advanced cervical cancer is usually treated with brachytherapy using an intracavitary applicator (Figure 1). MRI guided brachytherapy can be performed by imaging with the applicator in place prior to dose planning and treatment. This study evaluates the amount of distortion in DW images in vivo at both 1.5T and 3T MRI. DWI was performed in six patients at 1.5T MR and in two patients at 3T MRI. All MRI examinations were performed with the plastic applicator for brachytherapy in place. The cervix and lower uterus was manually contoured on T2 weighted images (T2W) and on DW images with b-value = 0 s/mm2 (Figure 2). The contours were compared by calculating the Jaccard similarity coefficient (the common area compared to the union area). The center of the applicator tandem was identified and marked on T2W and DW images and the shift was calculated. The Jaccard coefficient (mean±std.dev.) was 73.6±8.3 (1.5T ) and 78.5±3.8 (3T). The difference between the location of the tandem center was (mean±std.dev.) 2.2±1.2 mm (1.5T) and 1.5±1.6 mm (3T). If DW images should be used dose planning of brachytherapy the shift and distortion should be corrected to match the morphological images. © 2011 Springer-Verlag.