Table 2.

Taxonomy of segmentation regions.

Organ at risk	Total number of labeled slices included	Anatomical landmarks and definition
Brain	11,476	Sits inside the cranium and includes all brain vessels excluding the brainstem and optic chiasm.
Brainstem	34,794	The posterior aspect of the brain including the midbrain, pons, and medulla oblongata. Extending inferior from the lateral ventricles to the tip of the dens at C2. It is structurally continuous with the spinal cord.
Cochlea-left	4526	Embedded in the temporal bone and lateral to the internal auditory meatus.
Cochlea-right	4754	Embedded in the temporal bone and lateral to the internal auditory meatus.
Lacrimal-left	17,186	Concave-shaped gland located at the superolateral aspect of the orbit.
Lacrimal-right	17,788	Concave-shaped gland located at the superolateral aspect of the orbit.
Lens-left	3006	An oval structure that sits within the anterior segment of the orbit. Can be variable in position but never sitting posterior beyond the level of the outer canthus.
Lens-right	3354	An oval structure that sits within the anterior segment of the orbit. Can be variable in position but never sitting posterior beyond the level of the outer canthus.
Lung-left	8340	Encompassed by the thoracic cavity adjacent to the lateral aspect of the mediastinum, extending from the first rib to the diaphragm excluding the carina.
Lung-right	9158	Encompassed by the thoracic cavity adjacent to the lateral aspect of the mediastinum, extending from the first rib to the diaphragm excluding the carina.
Mandible	25,074	The entire mandible bone including the temporomandibular joint, ramus, and body, excluding the teeth. The mandible joins to the inferior aspect of the temporal bone and forms the entire lower jaw.
Optic-nerve-left	3458	A 2 to 5 mm thick nerve that runs from the posterior aspect of the eye, through the optic canal and ends at the lateral aspect of the optic chiasm.
Optic-nerve-right	3012	A 2 to 5 mm thick nerve that runs from the posterior aspect of the eye, through the optic canal and ends at the lateral aspect of the optic chiasm.
Orbit-left	8538	Spherical organ sitting within the orbital cavity. Includes the vitreous humor, retina, cornea, and lens with the optic nerve attached posteriorly.
Orbit-right	8242	Spherical organ sitting within the orbital cavity. Includes the vitreous humor, retina, cornea, and lens with the optic nerve attached posteriorly.
Parotid-left	8984	Multi-lobed salivary gland wrapped around the mandibular ramus. Extends medially to the styloid process and parapharyngeal space. Laterally extending to the subcutaneous fat. Posteriorly extending to the sternocleidomastoid muscle. Anterior extending to posterior border of the mandible bone and masseter muscle. In cases where the retromandibular vein is encapsulated by parotid, this is included in the segmentation.
Parotid-right	11,752	Multi-lobed salivary gland wrapped around the mandibular ramus. Extends medially to the styloid process and parapharyngeal space. Laterally extending to the subcutaneous fat. Posteriorly extending to the sternocleidomastoid muscle. Anterior extending to posterior border of the mandible bone and masseter muscle. In cases where the retromandibular vein is encapsulated by parotid this is included in the segmentation.
Spinal-canal	37,000	Hollow cavity that runs through the foramen of the vertebrae, extending from the base of skull to the end of the sacrum.
Spinal-cord	37,096	Sits inside the spinal canal and extends from the level of the foramen magnum to the bottom of L2.
Submandibular-left	10,652	Sits within the submandibular portion of the anterior triangle of the neck, making up the floor of the mouth and extending both superior and inferior to the posterior aspect of the mandible and is limited laterally by the mandible and medially by the hypoglossal muscle.
Submandibular-right	10,716	Sits within the submandibular portion of the anterior triangle of the neck, making up the floor of the mouth and extending both superior and inferior to the posterior aspect of the mandible and is limited laterally by the mandible and medially by the hypoglossal muscle.