Lattice strain evolution during deformation processing of Ti-Al alloys at high temperature is important in terms of its microstructural evolution and microstructural stability. It is shown here that careful evaluation of lattice parameters is critical for the understanding of thermal expansion, crystallographic order, chemical composition and response to pressure, allowing to identify phase transitions and segregation, in addition to the measurement of the more conventional quantities phase composition and order parameter. The lattice parameters of Ti-45Al-7.5Nb-0.25/0.5C (at. %) alloys were calculated using both Rietveld and single peak fitting methods from data obtained by in-situ synchrotron diffraction experiments at high temperature under atmospheric and high pressure respectively. The lattice strain evolution as a function of temperature in a Ti-45Al-7.5Nb-0.25C (at. %) alloy under high pressure was compared with that of a Ti-45Al-7.5Nb-0.5C (at. %) alloy heated under atmospheric pressure. The contribution of each of the four lattice strain factors is semi-quantitatively assessed in the temperature range investigated.