Optimizing packing contrast for MRI-based intracavitary brachytherapy planning for cervical cancer

Purpose: We prospectively tested five variations in vaginal gauze packing in an effort to improve contrast between the packing, cervix, and applicator for MRI-based intracavitary brachytherapy planning. Methods and materials: Five patients enrolled on a prospective study from May 2013 to October 2013 received MRI-based intracavitary brachytherapy for cervical cancer with variations of impregnated gauze packing. Substances tested included antibiotic cream alone, antibiotic cream mixed with ultrasound gel, conjugated estrogens cream mixed with ultrasound gel, ultrasound gel alone, and gadolinium. Images from the T2-weighted pelvic MRI were used to obtain signal intensity measurements at points within the packing, cervix, and applicator. Signal intensity values were normalized using the signal-to-noise ratio and compared using an unpaired t-test. Results: Ultrasound gel-impregnated gauze allowed for the greatest contrast between the packing and the cervix with a difference in mean normalized signal intensity of 38.2 (p < 0.01). Conjugated estrogens cream mixed with ultrasound gel and gadolinium also provided contrast when compared with cervix, with differences in mean normalized signal intensity of 25.3 and -16.2, respectively (p < 0.01 for both). For all variations but gadolinium, the normalized mean signal intensity of the packing was found to be significantly different from the applicator, with the ultrasound gel again demonstrating the greatest contrast with a difference of 42.5 (p < 0.01). Conclusions: Gauze impregnated with ultrasound gel, conjugated estrogens cream mixed with ultrasound gel, and gadolinium allowed for a significant difference in MRI signal intensity between the packing and the cervix. With respect to both the cervix and the applicator, ultrasoundgel-impregnated gauze provided the best contrast overall.