Both the IGES (.igs, .iges) and Parasolid (.x_t, .x_b) CAD formats are well supported in modern 3D/CAD software, so you shouldn't have trouble in find a program or converter that can perform igs to x_t conversion. Used to transfer CAD designs or models from one platform to another.
Open IGS file Open X_T fileA set of 3D modeling tools
A 3D product data optimalization software
A CAD conversion software
A CAD visualizaton, analyzation and translating system
A CAD/CAM software used to create 3D models
A suite of CAD applications
A dedicated CAD converter