[Design planning target volumes (PTVs) in intensity-modulated radiotherapy for nasopharyngeal carcinoma].

Background & Objective: Intensity-modulated radiotherapy (IMRT) may help to diminish radiation-induced normal tissue damage and improve quality of life of nasopharyngeal carcinoma (NPC) patients. However, highly conformal treatment techniques commonly establish steep dose gradients between tumor and normal tissues, therefore, daily setup variations can significantly compromise the ultimate precision of idealized IMRT delivery. This study was to investigate the setup accuracy of thermoplastic masks used for immobilizing NPC patients treated by simultaneous integrated boost IMRT, and to determine adequate margins to account for those uncertainties.