Purpose: To assess the feasibility of using diffusion tensor MRI (DT-MRI) to define the boundary of clinical target volume (CTV) in soft-tissue sarcoma (STS). In muscles, microscopic tumor invasion occurs preferably along muscle fibers. Therefore, anisotropic properties of the invaded tissues must be taken into account in order to accurately define the CTV as it receives a high curative radiation dose.
Methods: For our pilot study, we recruited eight healthy volunteers, five men and three women, and acquired MR images of the left and right thigh. The imaging session consisted of (a) two high resolution anatomical MRI scans (spin-echo, SE), T1- and T2-weighted; (b) a diffusion weighted (DW) SE scan using an echo planar (EP) acquisition with fat suppression. DT-MRI data was used as a geometry encoding input to solve the anisotropic Eikonal equation with Hamiltionian Fast-Marching method. The CTV boundary was determined by iso-levels of the solution being a map of fastest paths between image voxels. The assumption of the model is that preferential tumor spread occurs along the directions of the largest water diffusivity.
Results: T1-weighted acquisitions were used to match anatomical locations of the muscles in DT-MR images by means of manual segmentation of individual muscles. The fastest path maps were calculated within each muscle. Anisotropy of the iso-levels was compared across muscles with different anatomical orientation within the thigh, between muscles in left and right thighs of each subject and between muscles of different subjects. Analysis showed a high level of consistency on all levels.
Conclusion: Our feasibility study with healthy volunteers shows the promise of diffusion weighted MRI data for automated generation of anisotropic CTV boundary in STS. The iso-levels and the diffusion tensor eigenvalues ratio can be used as two controlling parameters for the extend and shape of the CTV.
Not Applicable / None Entered.