How to find each organ on CT, in DoseLab's own words, with the published source behind every boundary. Always check the protocol you are planning to.
The nerves that run from the neck into the arm. They control the muscles of the shoulder, arm and hand and carry feeling back from them.
The plexus is hard to see on CT, so Brouwer 2015 defines it by the anatomy around it (Table 1):
On the lowest slices, where the plexus wraps around the vessels, the vessels are included in the contour. Brouwer's supplement gives a step-by-step technique based on the Hall 2008 method. Sources commonly define the plexus per side.
The carotid arteries carry blood from the heart to the brain (internal carotids) and to the face and neck (external carotids).
Brouwer 2015 includes the common and internal carotid arteries and leaves out the external carotid.
The upper part of the food pipe. It carries food and liquid from the throat down into the chest.
In Brouwer 2015:
Just above it, Brouwer contours a separate cricopharyngeal inlet — the transition from the pharyngeal constrictors into the esophagus. It runs from the bottom of the arytenoid cartilages to 1 cm below the cricoid, with the tracheal lumen in front and the vertebral body behind.
RTOG 0920 defines the cervical esophagus as a tubular structure from the bottom of its pharynx structure to the thoracic inlet, so check which definition your protocol uses. Christianen 2011 covers the swallowing structures.
The voice box. The vocal cords make the voice, and the larynx closes over the airway during swallowing so food and liquid do not go into the lungs.
Brouwer 2015 splits the larynx into two structures (Table 1), following Christianen 2011 for the supraglottic part.
Supraglottic larynx
Glottic area (the vocal cords and the fat around them, with the air left out)
RTOG 0920 instead defines a single glottic/supraglottic larynx (GSL) structure from just below the hyoid to the cricoid cartilage — check which your protocol uses.
The lips close the mouth, keep food and saliva in, and help with speech and facial expression.
Brouwer 2015 runs the lip contour from the lower edge of the nose to the top of the mandibular body, and includes the inner surface of the lips (Table 1):
The mucosa in front of the jaws belongs to the lips; the mucosa to the side belongs to the buccal mucosa. RTOG 0920 asks for the lips and oral cavity as two separate structures.
The lower jaw. It holds the lower teeth and moves for chewing, speaking and swallowing.
Brouwer 2015 contours the entire mandible bone, without the teeth, and recommends a CT bone window. RTOG 0920 likewise includes the entire bony mandible from the TMJ through the symphysis.
Where food is chewed, mixed with saliva and tasted, and where swallowing begins. The tongue is also essential for speech.
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):
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.
Each parotid makes saliva and delivers it into the mouth through a duct that opens inside the cheek. Parotid saliva is thin and watery, and it supplies much of the flow while you eat. Saliva moistens food for chewing and swallowing, starts the digestion of starch, helps with taste and speech, and protects the teeth and lining of the mouth.
The Brouwer 2015 consensus defines the parotid on CT by the structures that surround it. In its boundary table:
The guideline includes the retromandibular vein in the contour, because it is hard to tell apart from gland tissue on a non-contrast CT, and its remarks list the carotid artery and the extracranial facial nerve as included too. It strongly recommends a planning CT with IV contrast to see where the gland ends. Protocols differ on whether the parotid excludes the part overlapping the target — check your protocol.
Three overlapping muscles that squeeze food and liquid down from the mouth into the esophagus when you swallow.
Brouwer 2015 contours the constrictors as one structure, about 3 mm thick:
Note on the lower limit: Brouwer's text places it at the lower edge of the cricoid cartilage, while its Table 1 lists the lower edge of the arytenoid cartilages (where its separate cricopharyngeal inlet structure begins). Published guidelines vary most at the top and bottom of this structure, so check which definition your protocol uses. Brouwer notes the constrictors can be subdivided for research — Christianen 2011 is one such reference.
The spinal cord carries signals between the brain and the body — for movement, feeling and reflexes.
For head and neck cases, Brouwer 2015 contours the true spinal cord, not the spinal canal:
Definitions differ between sources. For nasopharynx cases, Sun 2014 contours the visible true cord from the foramen magnum to 2 cm below the lower edge of the head of the clavicle, excluding the subarachnoid space. Some sources use the bony spinal canal instead. A limit only makes sense on the structure it was written for, so check the definition in the source behind your limit. Many clinics also add a PRV.
Salivary glands under the floor of the mouth. They produce much of the saliva that keeps the mouth moist between meals.
Brouwer 2015 gives these boundaries (Table 1):
The thyroid gland makes thyroid hormone, which sets the pace of the body's metabolism.
Brouwer 2015 describes the thyroid as two connected lobes located below the thyroid cartilage. It stands out well from the tissue around it on CT. Brouwer gives no further boundary table for it.
The published guidelines and atlases cited in the guides above. Open the original for the full boundary tables and images.
Consensus CT delineation guidelines for head and neck organs at risk from eight cooperative groups, with anatomical descriptions and example images. Citation checked against Crossref; content not yet reviewed by DoseLab.
Describes and validates a standardized CT-based method for delineating the brachial plexus, developed in patients treated with IMRT for head and neck cancer.
CT-based guidelines for delineating the organs at risk involved in swallowing. Citation checked against Crossref; content not yet reviewed by DoseLab.
Compares published contouring methods for the temporal lobe, middle and inner ear, parotid gland and spinal cord in nasopharynx cancer, recommends one method for each (Table 3), and provides a CT–MRI atlas of 33 organs at risk. Citation checked against Crossref; the temporal lobe and spinal cord recommendations were read in the open-access full text.