Penile traction therapy and Peyronie's disease: a state of art review of the current literature (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3547530/)
Here's a link to a recent (Feb 2013) research paper on the effectiveness of traction devices for Peyronies Disease, which analyzes the outcomes of several studies, including ones by Dr. Levine.