Modelling of LHCD with transport calculations is performed with the JETTO transport code, which has been upgraded by implementing the Fast Ray Tracing Code to calculate self-consistent LH power deposition profiles. Heat and particle transport models that are able to reproduce the experimental JET temperature and density profiles are used in JETTO for predictive high performance modelling. Application of 3.5 MW LHCD power provides an inverted q profile across 50-70% of the plasma radius whereas, without LHCD, the q profile is monotonic during the flat-top phase. The results predict that the fusion power is about 60% higher for high performance DT plasmas in the optimized shear scenario with 3.5 MW LHCD applied during the high performance phase than without LHCD at Bt = 3.4 T and Ip = 3.9 MA on JET. In addition, the width of the internal transport barrier (ITB) is 0.25-0.30 m larger and the ITB can be sustained for a longer time with LHCD.