The behavior of the Peierls structural transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide (TTT2I3) for different values of carrier concentration is analyzed in 3D approximation. In the frame of the physical model, two the most important electronphonon interactions are considered. The first interaction is of deformation potential type and the second one is of the polaron type. The scattering on structural defects is also taken into account, and it is shown that this interaction is very important for the explanation of the Peierls structural transition in TTT2I3 crystals. The renormalized phonon spectrum is calculated in random phase approximation. It is shown that the transition is of Peierls type and strongly depends on iodine concentration. The Peierls critical temperature is determined. In [1] the same dependences for 2D physical model are presented. It is demonstrated that the holephonon interaction and the interaction with the structural defects diminish the renormalized phonon spectrum and reduce the sound velocity in a large temperature interval.