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Table 2 Short description of delineation guidelines per organ at risk, the errors delineated and possible consequences

From: Interobserver variability in organ at risk delineation in head and neck cancer

Organ at risk International consensus guidelines [18] Errors Consequences of errors
Brainstem Cranial: bottom section of the lateral ventricles
Caudal: tip of the dens of C2
Cranial: start when the brainstem becomes visible (all RO)
Caudal: different interpretation of “tip” so a few slices difference
No impact on relevant dose parameter for precise NTCP (Dmax), depending on tumour location. But can effect estimated dose to spinal cord which has a more strict dose constraint
Cochlea CT scan in bone setting, cochlea in temporal bone Incorrect location (2 RO)
Entire petrous part of the temporal bone delineated (3 RO)
Effect on dose when wrong location is delineated
Difference in volume can have an impact on Dmean and Dmax depending on tumour location
Glottic area Cranial: cranial tip of arytenoids
Caudal: caudal edge of thyroid cartilage
Posterior: cricoid, anterior border of arytenoids
Enclosed by the thyroid cartilage
Entire larynx delineated, starting caudal of the hyoid and including the thyroid cartilage and arytenoids (2 RO)
Included caudal part of supraglottic larynx (2 RO)
Included arytenoids (2 RO)
Impact on relevant dose parameter for precise NTCP (Dmean)
Mandible CT scan in bone setting
Excluding teeth, including mandibular condyles and coronoid process
Teeth included (not systematically, but some RO in some cases)
Mandibular condyles and coronoid process not included (1 RO systematically)
No impact on relevant dose parameter for precise NTCP (Dmax), depending on tumour location
Oral cavity Cranial: Hard palate mucosa and mucosal reflections near the maxilla
Caudal: base of tongue mucosa and hyoid posteriorly and the mylohyoid and anterior belly of the digastric muscle anteriorly
Anterior and lateral: inner side of the mandible and maxilla
Posterior: soft palate, uvula and base of tongue
Included teeth (two RO)
Included the buccal mucosa (1 RO)
Excluded posterior part of oral cavity (1 RO)
Excluded base of tongue (1 RO)
Impact on relevant dose parameter for precise NTCP (Dmean)
Parotid gland Cranial: external auditory canal, mastoid process
Caudal: posterior part submandibular space
Anterior: Masseter muscle, posterior border mandibular bone, pterygoid muscle (med. and lat.)
Posterior: sternocleidomastoid muscle, lateral side posterior belly digastric muscle
Lateral: platysma and subcutaneous fat
Medial: Posterior belly of the digastric muscle, styloid process, para-pharyngeal space
Cranial and caudal borders varied up to a few slices between RO
Anterior: sometimes inclusion of the masseter and pterygoid muscles
Medial: digastric muscle sometimes included
Impact on relevant dose parameter for precise NTCP (Dmean)
PCM inferior [21] Caudal: lower edge of arytenoids
Cranial: first slice caudal to the hyoid bone
Caudal: several slices difference between RO Impact on relevant dose parameter for precise NTCP (Dmean)
PCM middle [21] Cranial: cranial border of C3
Caudal: caudal border of hyoid bone
Cranial: cranial border stopped at caudal border of C3 (3 RO). Only 2 RO delineated cranially enough Impact on relevant dose parameter for precise NTCP (Dmean)
PCM superior [21] Cranial: tips of the pterygoid plates (hamulus)
Caudal: caudal border of C2
Cranial: 1 RO delineated the superior muscle up to the base of skull Impact on relevant dose parameter for precise NTCP (Dmean)
Spinal cord Spinal cord, not canal
Cranial: tip of dens of C2
Caudal: At least cranial edge of T3, lower for more caudal tumours
Spinal canal delineated (2 RO)
Cranial: some difference depending on what was interpreted as “tip” of dens of C2
Caudal: not caudal enough, stopped several slices too high (3 RO, each in one patient)
No impact on relevant dose parameter for precise NTCP (Dmax), depending on tumour location. But can effect estimated dose to brainstem which has a less strict dose constraint
Submandibular gland Cranial: medial pterygoid muscle and mylohyoid muscle
Caudal: fatty tissue
Anterior: lateral surface mylohyoid muscle and hyoglossus muscle
Posterior: para-pharyngeal space, sternocleidomastoid muscle
Lateral: medial surface medial pterygoid muscle, mandible, platysma
Medial: lateral surface mylohyoid muscle, hyoglossus muscle, superior and middle PCM, anterior belly digastric muscle
Cranial: some variation in cranial border between RO Impact on relevant dose parameter for precise NTCP (Dmean)
Supraglottic larynx Cranial: tip of epiglottis
Caudal: cranial edge of arytenoids
Posterior: inferior PCM, pharyngeal lumen
Confined by the thyroid cartilage and hyoid bone, exclude pharyngeal lumen
Cranial: entire pharyngeal lumen delineated at the tip of the epiglottis (1 RO)
Caudal: delineation 2–3 cm more caudal than guidelines (2 RO)
Impact on relevant dose parameter for precise NTCP (Dmean)
  1. For detailed description of contour guidelines, see Brouwer et al. [18] and Christianen et al. [21]
  2. NTCP normal tissue complication probability, Dmean mean dose, Dmax maximum dose, PCM pharyngeal constrictor muscle, RO radiation oncologist