It may not be as easy to read, but combining the three RUN statements together saves you some substantial megabytes:
ctop_deb_orig latest 149596353f88 4 seconds ago 187 MB
ctop_deb_new latest d01f954b3adc 2 minutes ago 139 MB
This is because each RUN statement is creating a whole new layer in the image, so you're actually hanging on to all the stuff you were trying to get rid of!
Scott