Self-consistent time-dependent thermonuclear burn calculations were performed in order to investigate the potentiality of the proton-boron fuel for inertial confinement fusion. The results were compared with the approximate ones obtained by maximization of the ratio of thermonuclear energy to bremsstrahlung loss energy without consideration of the change in the ion and electron temperatures as well as of the change in the boron and proton concentrations caused by the burning process. It was found that for the initial conditions used, the simple approach represents an overestimate and that, in fact, the ratio of thermonuclear energy to bremsstrahlung losses is close to but smaller than unity. Thus, the question of ignition of pB11 in inertial confinement fusion remains open.