Table 5. Differences of delineation of clinical target volume (CTV, for CTV2) in intensity-modulated radiotherapy for NPC in different cancer centers.

Region	RTOG0615[23]	Singapore[4]	Hong Kong[3]	Fuzhou[5]	Chinese guideline[22]
Nasal cavity	Posterior 1/4–1/3	Posterior 1/3	Posterior 1/3	5 mm anterior to the posterior nasal aperture	Posterior part
Maxillary sinus	Posterior 1/4–1/3	Posterior 1/3	Posterior 1/3	5 mm anterior to the maxillary mucosa	5 mm anterior to the maxillary mucosa
Clivus	Anterior 1/2–2/3 (entire if involved)	Anterior 1/2 (entire if involved)	Anterior 1/2 (entire if involved)	Anterior 1/3	Anterior 1/3
Foramen ovale	Bilaterally	Bilaterally	Bilaterally	–	Bilaterally
Sphenoid sinus	Inferior part (entire in T3–T4 disease)	Included	Included	Inferior part (entire if involved)	Inferior wall/basis
Cavernous sinus	Included in high-risk patients (T3, T4, bulky disease involving the roof of the nasopharynx)	Included	Included	Inferior part	–
Retropharyngeal lymph node	Bilaterally (skull base to cranial edge of the hyoid)	Bilaterally (skull base to the level of the hyoid)	Bilaterally (skull base to the bottom of the hyoid)	Bilaterally (skull base to cranial edge of C2)	Bilaterally (skull base to caudal edge of C2)
Levels II–V	Bilaterally	Bilaterally	Electively irradiated	Bilaterally	Electively irradiated
Level Ib	Bilaterally included in node-positive patients	Included if the ipsilateral neck involved	Electively irradiated	–	Electively irradiated