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Purpose Diffusion-weighted ( DW) MRI, showing high contrast between tumor and background tissue, is a promising technique in radiotherapy for tumor delineation. However, its use for head-and-neck patients is hampered by poor geometric accuracy in conventional echo planar imaging ( EPI) DW- MRI. An alternative turbo spin echo sequence, DW- SPLICE, is implemented and demonstrated in patients. Methods The DW- SPLICE sequence was implemented on a 3.0 T system and evaluated in 10 patients. The patients were scanned in treatment position, using a customized head support and immobilization mask. Image distortions were quantified at the gross tumor volume ( GTV) using field map analysis. The apparent diffusion coefficient ( ADC) was evaluated using an ice water phantom. Results The DW images acquired by DW- SPLICE showed no image distortions. Field map analysis at the gross tumor volumes resulted in a median distortion of 0.2 mm for DW- SPLICE, whereas for the conventional method this was 7.2 mm. ADC values, measured using an ice water phantom were in accordance with literature values. Conclusions The implementation of DW- SPLICE allows for diffusion-weighted imaging of patients in treatment position with excellent geometrical accuracy. The images can be used to facilitate target volume delineation in RT treatment planning. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: The aim of this study is to assess the geometric accuracy of diffusion weighted (DW)-MRI by quantification of geometric distortions in the gross tumor volume (GTV) in head and neck (HN) cancer. Materials & Methods: A retrospective analysis was performed on the data of 23 patients (with 24 lesions). For these patients, magnetic field maps and DW-MRI were acquired. The magnetic field maps were converted to voxel displacement maps. GTV delineations were transferred onto these voxel displacement maps and the voxel shifts in the GTV were analyzed. Results: The median shift was 3.2mm and the maximal posterior and anterior shifts were up to 15.0 and 26.0mm respectively. The range of shifts varied from 11.8 to 25.6mm. The percentage of GTV voxels that showed a shift of at least 6mm was found to be 23.2%. Conclusions: Current DW-MRI images of HN tumors show severe distortions up to centimeters, which restrict the use of DW-MRI scans for GTV definition in RT treatment planning. [Copyright &y& Elsevier]