Preliminary results of a new workflow for MRI/CT-based image-guided brachytherapy in cervical carcinoma

Purpose We propose a method of image-guided brachytherapy (IGBT) that combines MRI-based target volume delineation for the first fraction with CT datasets of subsequent fractions, using an automatic, applicator-based co-registration, and report our preliminary experience. Materials and methods The MRI of the first fraction was used for the first brachytherapy planning. For each subsequent brachytherapy fraction, after the same applicator insertion, a new CT scan with the applicator in place was obtained. The MR image set was registered to the subsequent brachytherapy treatment planning CT using the applicator for rigid body registration. To demonstrate the registration quality, we used here the Dice index as a measurement of tandem delineation overlap between CT and MRI. Results The median Dice index was 0.879 (range 0.610–0.932), which indicated that the contours on CT and MRI fitted well. With this combination method, the median D90 of HR CTV and the calculated D2 cm 3 of the bladder, rectum, and sigmoid in each fraction were 7.2 (4.0–10.4), 5.9 (2.3–7.7), 4.0 (1.9–6.7), and 3.8 (0.6–7.2) Gy, respectively. Conclusion Our described method of MRI-guided IGBT offers a practical option for the benefits of target delineation.