SU‐G‐IeP1‐09: MRI Evaluation of a Direction‐Modulated Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer On 3T

Abstract

Purpose:To assess image quality and artifact extent of a novel direction modulated brachytherapy (DMBT) tandem applicator on a 3T MRI using various clinical imaging sequences.Methods:The tandem applicator is composed of a tungsten alloy with 6 peripheral grooves covered with a PEEK tip. An MR‐compatible phantom with similar dimensions to the female pelvis was manufactured. To visually assess the spatial shift of the applicator's tip, a mountable radial‐fiducial with 4 plastic rods, each of 3mm diameter, was designed to tightly fit on the applicator. The rods are separated by 16 mm and mounted at 90‐degree relative to one another. The pelvis phantom was filled with a solution of MnCl2 to mimic T2 relaxation time of the cervix (60‐80 ms at 3T).Imaging was performed on a 3T Philips Achieva using a 16‐channel Torso coil array. Four MR sequences were tested: T2‐weighted fast spin‐echo (T2w‐FSE), proton density weighted FSE (PDw‐FSE), T1‐weighted FSE (T1w‐FSE) and T1 weighted spoiled gradient echo (T1w‐GE). The spatial resolution was kept the same between all sequences: 0.6 × 0.6 × 3 mm3 with no slice gaps. Para‐sagittal images were acquired with the applicator fixed at a 30‐degree angle anterior to the B0‐ field to mimic clinical settings.Results:Minimal artifacts were observed on T2w‐FSE, PDw‐FSE and T1‐FSE, while significant artifacts were seen on T1w‐GE images. Artifacts induced in all 3 FSE sequences did not hinder accurate localisation of the tip and the applicator boundaries. The drift of the applicator's centreline from the radial fiducials was measured and found to be < 1 mm for the 3 FSE sequences.Conclusion:The tungsten–based DMBT applicator can be potentially used on 3T with various clinical sequences without inducing significant artifacts. Further validation on patients as well as the evaluation of relative SNR among the different sequences is required.