Comparison of positron emission tomography/computed tomography imaging and ultrasound in surveillance of head and neck cancer - The 3-year experience of the ENT Department in Poznan. - Wierzbicka M; Popko M; Piskadło K; Czepczyński R; Stankowska A; Piętka T; Dziuk M; Szyfter W (Reports of practical oncology and radiotherapy : journal of Greatpoland Cancer Center in Poznan and Polish Society of Radiation Oncology, 2011)