Recently it has been suggested that the presence of boron-11 during proton therapy leads to a significant dose increasement in the BUR. Three high-LET alpha particles with an average energy of 4 MeV are generated at the point of interaction between proton and boron-11. Nevertheless, the cross-section of p+B11→3α interaction is negligible and dose increasement is unlikely. The purpose of this study is dose evaluation of the proton therapy with and without the boron-11. All simulations were performed using MCNPX 2.6.0 code at the Snyder head phantom. At the elderly stage, the range of Bragg-peaks was adapted to the tumor volume, with and without boron-11. Then, the different concentrations of boron-11 were assumed including 65,500,10,10,2.5×10 and 5×10ppm in the tumor region. To investigate the maximum effectiveness of PBFT (proton boron fusion therapy), the entire tumor was assumed full of boron-11, and the dose components were calculated. Consequently, In the best case, the maximum dose amplification was less than 5%, in which the entire tumor was assumed full boron-11. The total number of alpha particles generated from p+B11→3α interaction is negligible. As well as the presence of boron-11 during the proton therapy makes that the Bragg-peaks happen in greater depth. Hence, from the Monte Carlo standpoint, the effectiveness of the proton boron fusion therapy is not related to the alpha particles because the dose component of alpha particles is negligible.