Having obtained his Masters in General Surgery in 1993, he went on to specialise in thoracic surgery at the renowned Memorial Sloan Kettering Cancer Center, New York from 1998 to 2000. Although he largely practised thoracic surgical oncology specialty at the NCCS from 2000 to 2014, he continued with emergency general surgical service at SGH, including trauma. In his tenure as the Head of Surgical Oncology at NCCS from 2008 to 2014, he repeatedly won awards for excellent service, exemplary educator and innovations in service improvement. Dr Koong is well known for improving medical practices at the department & management level and was the person one who initiated the smoke free pub legislation in Singapore. His practice consist of a combination of thoracic surgery and general surgery.