Comparison of apparent diffusion coefficient maps to T2-weighted images for target delineation in cervix cancer brachytherapy

Purpose: T2-weighted (T2W) magnetic resonance imaging (MRI) has been used for target delineation in cervix cancerbrachytherapy. The objective of this study was to examine the feasibility of using diffusion-weighted magnetic resonanceimaging (DWI) for target delineation as compared against T2W imaging. Material and methods: Fifteen cervix cancer patients, implanted with tandem and ovoid applicators, underwentT2W turbo-spin echo imaging and DWI with a maximum diffusion factor of 800 sec/mm2 on a 1.5-T MR scanner. Appa -rent diffusion coefficient (ADC) maps were derived from the DWI. The gross tumor volume was manually delineatedon the T2W and ADC datasets for each patient. The agreement between T2W- and ADC-delineated volumes was assessedusing the Dice similarity coefficient (DSC). An algorithm was developed to compare the edge contrast of the delineatedvolumes on T2W images and ADC maps by calculating the percentage difference in the intensity values of selectedregions of pixels inside versus outside the target contour. Results: ADC-delineated volumes were generally smaller than T2W-delineated volumes, yielding a low DSC of 0.54± 0.22. ADC maps were found to display superior definition of the target volume edge relative to T2W images, yieldinga statistically significant difference between the mean edge contrast on ADC (12.7 ± 7.7%) versus that on T2W images(4.6 ± 3.2%; p = 0.0010). Conclusions: These results suggest that incorporating the use of DWI for cervix cancer brachytherapy may yieldgross tumor volumes that are different from those based on T2W images alone.