  We derive compact expressions for one-loop scattering amplitudes of four
open-string vector bosons around supersymmetric configurations with
intersecting or magnetized D-branes on toroidal orbifolds. We check the
validity of our formulae against the structure of their singularities and their
behaviour under modular transformations to the transverse channel, exposing
closed string exchange. We then specialize to the case of forward scattering
and compute the total cross section for two massless open string vector bosons
on the brane to decay into closed strings in the bulk, relying on the optical
theorem. Although not directly related to collider signatures our predictions
represent a step forward towards unveiling phenomenological implications of
open and unoriented superstrings
