By Steve Ginsburg WASHINGTON (Reuters) - A "thorough and aggressive review" needs to be done to protect clean athletes from "gangsters" after a blockbuster report surfaced alleging widespread doping in athletics, the head of the U.S. Anti-Doping Agency (USADA) said on Sunday. Britain's Sunday Times newspaper and Germany's ARD/WDR broadcaster said they had obtained the secret data from the global athletics governing body, the IAAF, showing that endurance runners suspected of doping have been winning a third of Olympic and world championship medals. USADA Chief Executive Travis Tygart said he was unaware of any American involvement in the report but was disturbed by the allegations overall. More...