A radiation oncologist's guide to contour the parotid gland.

The parotid gland is the largest of the salivary glands and is primarily responsible for salivation and prevention of dry mouth as well as oral health. Routinely, the parotid gland is near target in head and neck cancer cases. It is critical that attention be given to avoid unnecessary dose to the parotid glands to preserve saliva, taste, and oral health. The facial nerve (CN VII) passes through the gland and divides it into the superficial and deep lobes. Anteriorly, it overlies the lateral surface of the masseter muscle; laterally, it is surrounded by subcutaneous fat planes of the cheek; and posterosuperiorly, it is bounded by the external auditory canal. The deep lobe is medial to CN VII and is bound by the parapharyngeal space medially, the mastoid process of the temporal bone posteriorly, and the ramus of the mandible anteriorly. Superiorly, the deep lobe extends to the level of the stylomastoid foramen.1,2 It should be noted that, inferiorly, below the angle of the mandible, the parotid tail inserts between platysma and sternocleidomastoid muscle in the area of the posterior submandibular space. Although the gland is divided into the 2 lobes, this anatomical distinction does not aid in the contouring process. However, the retromandibular vein, which is seen coursing through the deep lobe just along the medial margin of CN VII, may be useful for the radiation oncologist. There may be circumstances in which it would