Familial Nasopharyngeal Carcinoma 6

226 J. J. Lu, V. Grégoire, and S. Linmarginal local recurrence with a component ofrecurrent foci in the GTV. Isolated recurrence at theedge of the delineated PTV was not seen. Reduced-CTV described above seems to be acceptable forradiation therapy for NPC using IMRT. However,whether this strategy of CTV delineation was trulysufficient or the superb local control rate was due tohigh collateral dose encompassing the tissues next todelineated CTV is unknown.17.4Target Volume Selection and Delineationin the Neck17.4.1Diagnosis of Cervical Lymph AdenopathyUnlike the primary lesion, cervical lymph nodes involvementis largely determined based on the size (shortestaxis) of the lymph node(s) in head and neck cancers,and nodes are considered metastatic if their shortestaxis is ≥11 mm in the jugulodigastric regions, or >10 mmin other cervical regions. In addition, a group of three ormore lymph nodes of borderline is considered metastatic(van der Brekel et al. 1990). Furthermore, alymph node is considered involved if there is evidenceof central necrosis or extracapsular extension (ECE)(van der Brekel et al. 1990; Som et al. 1992).The diagnosis of retropharyngeal lymphadenopathywarrant additional discussion. RLNs can bedivided into medial and lateral groups, and are exclusivelyexamined through image studies, and pathologicalconfirmation of its status is usually notfeasible. The diagnostic criteria of an involved lateralRLN also depends on the presence of central necrosis,extracapsular disease extension, and the size ofthe lymph node. However, RLNs atrophy with ageand are usually obliterated after 20 (Ogura et al.2004). The short axis of normal RLNs on MRI is usuallyshorter than 4.5 mm, according to large series ofpatients with NPC, and the authors recommendedthat lateral RLN should be considered as involved ifthe shortest axis is 5 mm or more (Lam et al. 1997;King et al. 2000). Literatures addressing medial RLNin NPC are limited, and medial retropharyngeallymphadenopathy are reported sporadically (Lam etal. 1997; Ng et al. 2006). As a medial RLN is usuallynot visible on CT or MRI in a normal individual, it isreasonable to consider any visible medial RLN on CTor MRI abnormal.Although CT or MRI of the head and neck areacan both be used for diagnosis and staging for NPC,MRI provides more superior sensitivity and specificityfor detecting cervical lymph adenopathy, includethose in the retropharyngeal region (Olmi et al. 1995;Ng et al. 1997).The accuracy of FDG-PET/CT in detecting cervicallymph adenopathy has been studied in a numberof clinical trials. Earlier reports indicated slightimprovements regarding sensitivity and specificityof FDG-PET over enhanced CT and MRI (Adams etal. 1998; Kau et al. 1999). However, the results of ameta-analysis recently reported by Kyzas et al. (2008)indicated that the sensitivity and specificity of FDG-PET/CT were 50% and 87% in head and neck cancerpatients with clinically negative neck. In addition,the utilization of FDG-PET/CT in the diagnosis andstaging specifically for nasopharyngeal carcinomahas not been fully addressed. Convincing results thatdemonstrate the additive value of PET/CT on top ofCT and MRI are needed before PET/CT can be routinelyrecommended for nasopharygneal cancer.17.4.2Patterns of Cervical Lymph Node MetastasesNasopharynx is a centrally located structure withextensive submucosal capillary lymphatic plexus.Partly due to this extensive lymphatic existence, NPChas a propensity of lymph node involvement in itsearly stages. Clinical evident cervical lymph adenopathyis seen in more than 85% of the patients withNPC (Tang 2009; Ng 2000). As a centrally locatedstructure, there is a high probability of bilateral necknode metastases, and up to 50% of the patients withcervical lymph node metastasis have bilateralinvolvement (Sham et al. 1990; Tang et al. 2009).Lymph node metastasis in NPC usually follows anorderly pattern, though three specific routes of lymphaticdrainage: the retropharyngeal nodes, jugulodigastricnodes, and deep posterior cervical nodes toother cervical nodal regions.17.4.2.1Retropharyngeal Lymph NodesRLN, especially those in the lateral group, provideone of the most important routes of spread in NPC.The incidence of RLN metastasis in NPC is