  We develop a novel approach to fusion reactions for syntheses of superheavy
elements, which combines the time-dependent Hartree-Fock (TDHF) method with a
dynamical diffusion model based on the Langevin equation. In this approach, the
distance of the closest approach for the capture process is estimated within
the TDHF approach, which is then plugged into the dynamical diffusion model as
an initial condition. We apply this approach to hot fusion reactions leading to
formation of the element $Z=120$, that is, the $^{48}$Ca+$^{254,257}$Fm,
$^{51}$V+$^{249}$Bk, and $^{54}$Cr+$^{248}$Cm reactions. Our calculations
indicate that the distances of the closest approach for these systems are
similar to each other and thus the difference in the probabilities of
evaporation residue formation among those reaction systems originates mainly
from the evaporation process, which is sensitive to the fission barrier height
and the excitation energy of a compound nucleus.
