Comparison of the MRI sequences in ideal fiducial maker-based radiotherapy for prostate cancer

Abstract

Prostate contouring using CT alone is difficult. To overcome the uncertainty, CT/MRI registration using a fiducial marker is generally performed. However, visualization of the marker itself can be difficult with MRI. This study aimed to determine the optimal MRI pulse sequence for defining the marker as well as the prostate outline among five sequences. Materials and methods:A total of 21 consecutive patients with prostate cancer were enrolled.Two gold fiducial markers were placed before CT/MRI examination. We used the following five sequences: T1-weighted spin-echo (T1WI; TR/TE, 400-650/8 ms); T2-weighted fast spin-echo (T2WI; 4000/80); T2*-2D-weighted gradient echo (T2*2D; 700/18); T2*-3D-weighted gradient echo (T2*3D; TR/TE1/deltaTE, 37/14/7.3); and contrast-enhanced T1-weighted spinecho (CE-T1WI; 400-650/8). Qualitative image analysis of the sequences was performed by three observers. These observers subjectively scored all images on a scale of 1-3 (1 = unclear, 2 = moderate, 3 = well visualized). A higher score indicated better visualization.Results: T2WI was significantly superior to the other sequences in terms of prostate definition. T2*2D and T2*3D were strongly superior to the other sequences and were significantly superior in terms of fiducial marker definition.Conclusions: T2*2D and T2*3D are superior to the other sequences for prostate contouring and marker identification. Therefore, we recommend initial T2*3D and T2*2D examinations.