Oral Pharynx Cancers

Radiation Therapy Techniques

Soft Palate

Soft palate cancers are treated to the primary site and bilateral neck. There is no data to support ipsilateral neck radiation in these patients. As with BOT lesiosn, IMRT can be used to spare the contralateral parotid in clinically negative necks.

2D fields are opposed lateral fields to the primary site and upper necks. Use a mask, biteblock and neck extension setup. The field should include the retropharyngeal nodes which are at risk for all soft palate cancers. Block the roots of the teeth and the EAC.

The low neck is treated with an AP field matched at the thyroid notch below the hyoid bone. Use a midline block to protect the spinal cord and glottic larynx. At 45 Gy, split the lateral fields to anterior photon and posterior electron field to protect the cord. Usually posterior neck electron energies of 9 MeV are used, but this may vary depending on individual anatomy. Fields should be reduced to areas of gross disease at the primary site and neck nodes concurrently with posterior neck electron irradiation.

Tonsil

Abite block is always used to spare the tongue. If there are metallic dental fillings, care should be taken to avoid irradiating them, if possible. If not, attenuators such as reinforced dental trays can be used to absorb scatter to minimize mucosities adjacent to these fillings. Doses to early stage lesions are 66 Gy, with more advanced leasions to 70 Gy. For microscopic disease, treat to 60 Gy, in the involved neck, boosting positive nodes.

Indications to treat the contralateral neck include:

primary lesion that crosses the midline
advanced ipsilateral neck disease in a clinically negative contralateral neck

The contralalteral jugular nodes may be treated up to the digastric muscle at the bottom of the C1 transverse process and the bilateral retropharyngeal chain can be covered.

Base of Tongue

BOT cancers are treated to the bilateral neck and primary lesions. There are no situations where the ipsilateral neck treatment is sufficient. The field junction is set above the larynx so as to protect the glottic larynx from radiation, using an anterior larynx block on the AP low neck field. Lateral opposed fields are used on the upper nekc and primary sites. Uninvolved bilateral neck nodes recieve 54 Gy at 1.8 Gy/fraction. .