In this paper, the in-medium NN - N Delta cross section is calculated in the framework of the one-boson exchange model by including the isovector mesons, i.e., delta and rho mesons. Due to the isospin exchange in the NN - N Delta process, the vector self-energies of the outgoing particles are modified relative to the incoming particles in isospin asymmetric nuclear matter, and it leads to the effective energies of the ingoing NN pair being different from the outgoing N Delta pair. This effect is investigated in the calculation of the in-medium NN - N Delta cross section. With the corrected energy conservation, the cross sections of the Delta(++) and Delta(+) channels are suppressed, and the cross sections of the Delta(0) and Delta(-) channels are enhanced relative to the results obtained without properly considering the potential-energy changes. Our results further confirm the dependence of medium correction factor R = sigma*(NN - N Delta)/sigma (free)(NN - N Delta) on the charge state of NN - N Delta especially around the threshold energy, but the isospin splitting of medium correction factor R becomes weak at high beam energies.
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