Former WCVB-TV (Channel 5) anchor Heather Unruh on Thursday emceed Boston Medical Center’s “Food for Thought’’ dinner, an annual fund-raiser for the hospital’s pediatric programs. It was one of Unruh’s first public appearances since she accused actor Kevin Spacey of sexually assaulting her teenage son on Nantucket two summers ago. Because a reception and dinner in a ballroom at the Mandarin Oriental Boston isn’t the place to talk about such a deeply personal issue, she didn’t. But Unruh did take a moment to address what she called “the elephant in the room,’’ telling the crowd: “I feel your support and love, and I thank you very much.’’ Unruh’s son, who was 18 at the time of his encounter with Spacey, is one of several boys and young men who allege the “House of Cards’’ star sexually harassed or abused them. Last week, the Old Vic theater in London said it had received 20 accounts of alleged inappropriate behavior by Spacey during his decade-long tenure as the theater’s artistic director. Spacey is currently in a rehab center in Arizona.