South Shore Medical Center, which serves 60,000 patients with offices in Norwell, Kingston, and Weymouth, is celebrating its 50th anniversary. The group practice founded by five physicians in 1962, including Arthur Garceau of Norwell, is planning a year of special events to mark the date. The center focuses on providing patients with a committed personal physician through all stages of life. It was one of the founding members in 2004 of Atrius Health, a nonprofit affiliation of six community-based medical groups now serving about 1 million adult and pediatric patients in Eastern and Central Massachusetts.