When a thief left Knox Community Hospital in Mount Vernon with a truckload of X-ray film last fall, hospital officials thought he was an employee of a recycling firm hired to dispose of the material. Hospital employees learned recently that the film actually was taken by an opportunistic criminal hoping to cash in on the silver contained in it, a growing type of theft that has struck health-care centers in surrounding states. Only limited patient information was contained on the film, such as patients' names, dates of birth and body parts identified, but hospital officials launched an investigation and notified police, Knox Community spokeswoman Prema Samhat said."Our staff is undergoing refresher training, and policies will be reviewed and revised as necessary to safeguard against future incidents," she wrote in a statement. "The hospital is reviewing its contracted services and considering options to do on-site document and film shredding."