Nasopharynx

Dos 543

Nasopharynx – Location

A cuboidal chamber located below the base of the skull and behind the nasal cavity; extends to the junction of C1–C2.

Borders of the Nasopharynx

• Anterior: Posterior choanae

• Posterior: Clivus and first two cervical vertebrae

• Superior: Body of the sphenoid

• Inferior: Soft palate

Epidemiology

Uncommon worldwide but common in China, Southeast Asia, and Eskimo populations; peaks in 4th–5th decade of life.

Major Etiologic Factors

• Viral: Epstein-Barr Virus (EBV)

• Genetic: HLA predisposition

• Environmental: Poor ventilation, exposure to smoke/dust, and diet

Most Common Histology

Epidermoid or squamous cell carcinoma (~90% of cases).

Common Lymphatic Spread

~85% present with lymphadenopathy; most commonly to retropharyngeal (69%) and level II cervical nodes (70%).

Preferred Treatment

Radiation therapy is the treatment of choice; chemotherapy often added for improved survival. Surgery resection is not possible.

Common RT Technique

IMRT is most commonly used, using shrinking field or simultaneous integrated boost techniques to cover large and complex volumes.

Target Volumes

Volumes include: nasopharynx, adjacent parapharyngeal tissues, cervical lymphatics (jugular, spinal accessory, and supraclavicular nodes), posterior ethmoid cells, sphenoid sinus, and basisphenoid, base of skull, posterior nasal cavity and maxillary antrum, and lateral and posterior pharyngeal wall to the lower pole of tonsil, in addition to the retropharyngeal, upper cervical, mastoid, and posterior cervical lymph nodes

Bilateral anterior supraclavicular nodes are always included

Typical Dose Prescription

66–70 Gy (2.0 Gy/fx) to the primary tumor site.

Field Border – Anterior

Posterior 2 cm of nasal cavity (or 2 cm beyond tumor extension); posterior 1/3 of maxillary sinus; posterior ethmoid sinuses; posterior ¼ of orbit.

Field Border – Posterior

Extends behind spinous processes to include retropharyngeal nodes, posterior pharyngeal wall, and deep cervical nodes.

Field Border – Superior

Includes entire sphenoid sinus, cavernous sinus, and base of skull with at least a 0.5 cm margin.

Lower Neck and Supraclavicular Coverage

Bilateral anterior supraclavicular nodes and lower cervical nodes are included due to high risk of spread.

Brachytherapy Use

May be used as interstitial or intracavitary implants or recently HDR afterloading to boost residual nasopharyngeal disease.