Use Of Diffusion-Weighted Imaging For Target Delineation In 3d-Mri Assisted Cervix Cancer Brachytherapy

Current GEC-ESTRO guidelines for image-guided brachytherapy (IGBT) recommend the use of T2-weighted magnetic resonance imaging (MRI) for target delineation. The objective of this study was to examine the feasibility of using diffusion- weighted imaging (DWI) for target delineation in IGBT when compared to T2-weighted imaging. Fifteen patients with stage IB1 - IIIB cervical cancer were scanned on a 1.5-T clinical scanner as part of brachytherapy planning. Scanning sequences included T2-weighted (T2) turbo-spin echo imaging (TR 4178 ms, TE 100 ms) and DWI (TR 1300 ms, TE 75 ms) with a maximum diffusion factor of 800 s/mm2. Images were acquired in the parasagittal orientation with a slice thickness of 0.5 cm, and in-plane resolution of 0.2 cm or less. Apparent diffusion coefficient (ADC) images were derived from the DWI. The gross tumor volume at time of brachytherapy was manually delineated on the T2 and also on the ADC image dataset for each patient. To quantify the strength of the tumor edge visible on T2 and ADC images, an algorithm was developed to track the contour on each image slice and calculate the percent difference in the intensity values of pixels inside versus outside the contour. Only intensities within a 3 x 3 pixel region centered about the contour were used in the calculation. The percent difference in tumor edge intensities was calculated in this manner for the T2- and ADC-delineated tumor volumes, and compared to one another. In addition, the agreement between T2- and ADC-delineated tumor volumes was assessed using the Dice similarity coefficient (DSC), defined as the ratio between the common and averaged volumes. There was a statistically significant difference between the mean tumor edge intensity on ADC (12.7 ± 7.7%) versus that on T2 images (4.6 ± 3.2%; p = 0.0007). On average, ADC-delineated tumor volumes were smaller than T2-delineated tumor volumes (81.1 ± 154.1 cc versus 94.4 ± 181.2 cc, p = 0.07). The average DSC between the ADC- and T2-delineated tumor volumes was 0.55 ± 0.22, where a DSC of 1.0 indicates perfect agreement. ADC images derived from DWI MR scans were found to display superior definition of the tumor edge relative to T2-weighted images. ADC-delineated gross tumor volumes were also found to be generally smaller and to highlight disease not visualized on T2-weighted imaging. These results suggest that incorporating the use of DWI into the GEC-ESTRO recommendations for IGBT may yield gross tumor volumes that are more consistent than those based on T2 images alone.