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) |