Oral Cavity

The space from the lips to the junction of the hard and soft palate above and the circumvallate papillae of the tongue below — including the oral tongue, floor of mouth, buccal mucosa and palate.

Where food is chewed, mixed with saliva and tasted, and where swallowing begins. The tongue is also essential for speech.

Dose to the oral cavity drives mucositis, taste change and pain during treatment, and affects eating long after. How it is evaluated depends on the subsite: when the oral cavity is not the primary site, it is a normal structure to keep low; when it is the primary site, only the part outside the target is evaluated, and the goal is higher.

Brouwer 2015 uses an extended oral cavity — the space behind the inner arch of the mandible and maxilla. It reaches back into the front of the oropharynx: Brouwer notes it can be split for research into oral tongue and anterior oropharynx by a line from the back of the hard palate to the hyoid. Its boundaries (Table 1):

• Top: the hard palate mucosa and the mucosal reflections near the maxilla.
• Bottom: the base of tongue mucosa and the hyoid at the back; the mylohyoid and the anterior belly of the digastric at the front.
• Front and sides: the inner surface of the mandible and maxilla.
• Back: the back edges of the soft palate and uvula, and lower down the base of tongue.

The mucosa in front of the jaws goes with the lips, and the mucosa to the side goes with the buccal mucosa. RTOG 0920 defines the oral cavity differently — for non-oral cavity cancers, as a composite of the anterior half to two-thirds of the oral tongue and floor of mouth, the buccal mucosa and the palate — so check which your protocol uses.