Radiation and Cancer Physics

PD 09 - Physics 5 - Poster Discussion - Imaging for Treatment Planning

1072 - A Preliminary Study on the Use of Multiplexed Sensitivity Encoding for Geometric Distortion Reduction in MRI Simulation in Radiation Therapy

Tuesday, October 23
1:00 PM - 1:06 PM
Location: Room 217 C/D

A Preliminary Study on the Use of Multiplexed Sensitivity Encoding for Geometric Distortion Reduction in MRI Simulation in Radiation Therapy
X. Chen, and J. Dai; National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Purpose/Objective(s): Single shot echo planar imaging(EPI) is commonly used for obtaining diffusion weighted image in radiotherapy, however the geometric distortion of single shot diffusion weighted imaging (SS_DWI) limits its utilities in precision radiotherapy. Multiplexed sensitivity-encoding (MUSE) is a novel interleaved DWI-EPI technique correcting nonlinear shot-to-shot phase variations without the need of navigator echoes. To the best of authors’ knowledge, MUSE_DWI has not been introduced and tested for the purpose of radiotherapy. This study was aimed to investigate using MUSE_DWI in reducing the geometric distortions for brain radiotherapy, based on both phantom and patient results.

Materials/Methods: In the phantom study, the phantom diameters measured in the MUSE_DWI and SS_DWI images were compared and the percentages of geometric distortion (%GD) were calculated. The shifting vectors of control points were also plotted and calculated. In the patient study, a total of 10 patients (6 with post-surgery glioma, 4 with brain metastasis tumor) who used MRI for target delineation were enrolled, and the image distortion levels in SS_DWI and MUSE_DWI were compared using T2 PROPELLER images as the reference. The tumor targets and 4 normal organs(brainstem, cerebellum, cerebrum, and Hippocampus) were delineated based on T2 PROPELLER, SS_DWI and MUSE_DWI respectively. The dice similarity coefficient (DSC) and the Hausdorff distance (HD) were used for quantifying the geometric distortion levels.

Results: In phantom study, the most prominent image distortion along the phase encoding direction measured by GD was 6% for SS_DWI and 2% for MUSE_DWI; the mean relative displacement of all control point was 4.45±3.44mm for SS_SWI, and 2.17±1.9mm for MUSE_DWI. For all the organs and targets involved, higher DSC values were obtained using MUSE_DWI than using SS_DWI with statistical significance (p<0.01); smaller HD were obtained with MUSE_DWI than using SS_DWI with statistical significance (p<0.01). The mean improvement of HD from SS_DWI was up to 3.65±1.31mm by using MUSE_DWI. For the ROIs selected, no difference was observed between the mean value and histogram of ADC maps from the two methods.

Conclusion: MUSE_DWI is a robust and promising technique for geometric distortion reduction in brain radiotherapy, as compared to SS_DWI. A dedicated receiver coils with high number of channels should be designed and introduced for the purpose of radiotherapy in future.

Author Disclosure: X. Chen: None. J. Dai: None.

Xinyuan Chen, PhD

Disclosure:
No relationships to disclose.

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