  Weak decay tree and annihilation - t-channel W - exchange amplitudes for the
D0 -> K0S pi+ pi- process are calculated using quasi two-body QCD factorization
approach and unitarity constraints. Final state strong kaon-pion and pion-pion
interactions in S, P and D waves are described through corresponding form
factors including many resonances. Preliminary results compare well with the
effective mass distributions of the Belle and BABAR Collaboration analyses.
