Hi Jose. in attentio to your post:

yes, I installed xfce4 with depinst command

this the output of the dependencies checking:

bash-4.3# prt-get depinst -if elementary-xfce-icon-theme
package elementary-xfce-icon-theme is installed
bash-4.3#

then I checked the dependencies:
bash-4.3# prt-get depends xfce4 | grep elementary-xfce
[i] elementary-xfce-icon-theme

then I tried to update and the end of the output is the following:

................................................................................................
WARNING: Footprint ignored.
Building '/home/pkgmk/pkg/elementary-xfce-icon-theme#0.5-1.pkg.tar.xz' succeeded.
prt-get: reinstalling elementary-xfce-icon-theme 0.5-1
gtk-update-icon-cache: Cache file created successfully.
gtk-update-icon-cache: Cache file created successfully.
gtk-update-icon-cache: No theme index file.
gtk-update-icon-cache: No theme index file.

-- Packages updated
elementary-xfce-icon-theme [post: failed]

prt-get: updated successfully
bash-4.3#

I remark that after the first xfce4 installation I had no problem with the icons. that happened after the first prt-get sysup

regards!