Utility of Positron Emission Tomography in Radiotherapy Practice with Emphasis on Head and Neck Cancer

Several issues related to functional imaging in treatment planning and response assessment in head and neck cancer exist. In the pre-radiotherapy setting, integrated positron emission tomography (PET)-computed tomography (CT) provides more accurate delineation of disease extent in head and neck cancer than does PET or CT alone, while fluorodeoxyglucose (FDG)-PET shows promise in detecting distant metastases and/or primary tumour after a negative work-up. Incorporating FDG-PET data during the radiotherapy planning stage may significantly alter the gross tumour volume as well as identify primary tumour sites. Given sufficient time following radiation therapy (RT), FDG-PET is valuable in identifying residual tumours where CT and/or magnetic resonance imaging are unable to. While FDG-PET and PET-CT show great potential, challenges exist in successfully integrating the data into radiotherapy planning. No integrated system is used throughout the planning and treatment delivery process, leading to difficulty in reconciling imaged data with accurate radiotherapy delivery. This is particularly true when attempting to accurately delineate the tumour boundary. Although the several discussed methods yield good results, target volume definition remains elusive and uncertain. By identifying targets using mathematical thresholding techniques some of this uncertainty is removed.