I don't understand your formula.
Where did you found that ?
I know 3 methods for LST calculation using Landsat thermal images:
1. the mono-window algorithm developed by Qin http://www.bgu.ac.il/bidr/research/phys/remote/Papers/2001-Qin_Mono_Window_IJRS_01.pdf
2. the Sobrino algorithm, by Sobrino et al. ftp://atmosfera.cl/pub/elias/Paula/2004_Sobrino_RSE.pdf
3. the Radiative Transfer Equation (RTE) http://www.uv.es/ucg/articulos/2005/Publications_2004_10.pdf and http://people.eri.ucsb.edu/~dozier/Pubs/WanDozierIEEE1989.pdf
So, what is your method ?