Familial Nasopharyngeal Carcinoma 6

Selection and Delineation of Target Volumes in Intensity-Modulated Radiation Therapy for Nasopharyngeal Cancer 221Table 17.4. Radiological boundaries of the retrostyloid space and supraclavicular fossaSpace Cranial Caudal Anterior Posterior Lateral MedialRetrostyoidBase of skull(jugular foramen)Upper limit oflevel IIParapharyngealspaceVertebral body/base of skullParotid spaceLateral edge ofRP notesSupraclavicularfossaLower border oflevel IV/VbSternoclavicularjointSCM m.; skin;clavicleAnterior edgeof posteriorscalenus m.Lateral edge ofposterior scalenusm.Thyroid gland/tractiesSCM sternocleidomastoid; RP retropharyngeal17.2.2.2Retrostyloid SpaceAccording to the Consensus, the cranial border of thelevel II lymph nodes is set at the lateral process of C1.However, the lymph nodes lie in the fatty space aroundthe jugulocarotid vessels up to the jugular foramen,i.e., the retrostyloid space (Table 17.4, Fig. 17.7) mayreceive a retrograde lymph flow from the level IInodes. In addition, direct extension of disease froman infected RLN to the retrostyloid space is notuncommon in NPC. In view of the high probability ofdisease metastasis to the retropharyngeal and level IIlymph nodes in NPC, it is reasonable to consider theretrostyloid space a high-risk region, although thesignificance of direct drainage from nasopharynx tothese nodes is unknown.17.2.2.3Supraclavicular Lymph NodesThe supraclavicular fossa in NPC was originally proposedby Ho et al. and is defined by three points: (1)the superior margin of the sternal end of the clavicle,(2) the superior margin of the lateral end of the clavicle,and (3) the point where the neck meets the shoulder(Ho 1978). This definition was adopted by thelatest version of the AJCC/UICC staging system of NPC(Greene 2002). Metastases to the supraclavicularlymph nodes in NPC is a strong indicator for distantfailure and poor prognosis, and is currently classifiedas N3 disease in the AJCC staging system for NPC. Ho’sdefinition of the supraclavicular fossa is clinical anddepends on the clinical examination. In an attempt toimprove the reliability of detecting the supraclavicularlymph adenopathy, Ng et al. (2007) replaced the clinicalboundaries of the supraclavicular fossa with radiologicallandmarks, and included only level IV and Vbas the supraclavicular nodal region. Such a simplificationremained predictive for both distant control andoverall survival. However, in the Robbins Classificationof cervical lymph node groups and in the Consensus,the supraclavicular fossa is not one of the neck levels(Grégoire et al. 2003). Grégoire et al. (2006) supplementedthe Consensus in the lymph node positive andthe postoperative neck by proposing criteria for thesupraclavicular fossa, which is bounded by the lowerborder of Level IV/Vb cranially, the sternoclavicularjoint caudally, thyroid gland/trachea medially, lateraledge of the posterior scalenus muscle laterally, anterioredge of posterior scalenus muscle posteriorly, andsterno-clado-mastoid muscle, skin, or clavicle anteriorly(Table 17.3, Fig. 17.8).17.3Target Volume Selection and Delineationof the Primary DiseaseThe International Commission on Radiation Unitsand Measurement (ICRU) Report No. 50 differentiatedtreatment planning volumes to GTV, CTV, andplanning target volume (PTV) (Fig. 17.9):GTV: all known gross disease, including abnormallyenlarged regional lymph nodes. To determineGTV, appropriate radiology examination must beused that give the maximum dimension of what isconsidered potential gross disease.CTV: encompass GTV plus regions considered toharbor potential microscopic disease.PTV: provides margin around CTV to allow forvariation in treatment setup and other anatomicmotion during treatment, such as respiration, does notaccount for treatment machine beam characteristics.The ICRU Report 62 introduced the internal targetvolume (ITV) to cover the physiological movementof the GTV and/or CTV. Since physiologicalmotion in the head and neck area is usually not