Efficacy and Safety of Tadalafil 20 mg on Demand vs. Tadalafil 5 mg Once-a-Day in the Treatment of Post-Radiotherapy Erectile Dysfunction in Prostate Cancer Men: A Randomized Phase II TrialUmberto Ricardi, A Tizzani, Patrizia Ciammella et al.|The Journal of Sexual Medicine|2010Cited by 32