  We investigate corrections to the handbag approach for wide-angle Compton
scattering off protons at moderately large momentum transfer: the photon-parton
subprocess is calculated to next-to-leading order QCD and contributions from
the generalized parton distribution E} are taken into account. Photon and
proton helicity flip amplitudes are non-zero due to these corrections which
leads to a wealth of polarization phenomena in Compton scattering. Thus, for
instance, the incoming photon asymmetry or the transverse polarization of the
proton are non-zero although small.
