Familial Nasopharyngeal Carcinoma 6

222 J. J. Lu, V. Grégoire, and S. LinFig. 17.7. Axial CT images of a patient with N0 neck withretropharyngeal and retrostyloid space delineated. The delineatedareas correspond to the CTV, thus no margins forset-up error was included. (Adopted from Grégoire et al.(2006). Used with permission from Elsevier)substantial after immobilization using thermoplasticmask, the significance of ITV in the radiation therapyof NPC is largely unknown.Accurate definition and delineation of the targetvolumes in the precise radiation therapy includingIMRT for the treatment of NPC is the single mostcritical factor for disease control. As the dose distributionbecomes more precise, underdosed irradiationof the diseased areas is detrimental to the diseasecontrol and thus patients’ survival. On the other hand,the nasopharynx is located adjacent to the criticalnormal organs and tissues such as brain, brainstem,spinal cord, pituitary, optic chiasm, parotid glands,etc. Unnecessary irradiation to these organs at risk