Blackbody energy density spectrum in four dimensions

I don’t know how to calculate the energy density in four dimensions. I know the density of states is
$$
g(varepsilon) = g_sfrac{4pi V}{h^3c^3}varepsilon^2; quad g_s = 2
$$
but it is only for three dimensions and I don’t know how to extend it to four dimensions.
Any advice will be very helpful. Thanks in advance