HYPOPHARYNX-TARGET VOLUME DELINEATION

Overview

• The hypopharynx lies between the oropharynx superiorly and the cervical esophagus inferiorly; superiorly it is defined by the top of the hyoid bone (~C4) and inferiorly by the bottom of the cricoid cartilage (~C6).
• It is part of the pharynx critical for speech and swallowing; tumours often disrupt both functions.
• Three subsites: paired pyriform sinuses, posterior pharyngeal wall, and the post-cricoid region.
• Tumours tend to have extensive submucosal spread and can involve multiple hypopharyngeal sites and adjacent soft tissue because anatomic barriers are minimal.
• Hypopharyngeal cancers have a high propensity for lymph node involvement due to a rich submucosal lymphatic plexus; bilateral cervical nodes and lateral retropharyngeal nodes are commonly involved.
• Posterior cricoid/post-cricoid tumours are less common; pyriform sinus is the most common site (65–85%)

Patterns of spread

Subsite	Patterns of spread / nodes
Pyriform sinus	Anteromedial: arytenoids, aryepiglottic folds, intrinsic laryngeal muscles (may cause vocal cord fixation), para-glottic space. Posterior: constrictor muscles, prevertebral tissue. Lateral: paraglottic space, thyroid cartilage and lateral neck. Superior: oropharynx, pre-epiglottic space, thyroid membrane. Inferior: post-cricoid area. Lymph nodes: commonly retropharyngeal (RP), II, III; other levels at risk include IV and V1 for inferior tumours involving the apex.
Posterior pharyngeal wall	Superiorly: extension to oropharynx. Inferiorly: extension to cervical esophagus. Posteriorly: pre-vertebral fascia and retropharyngeal space. Nodes: retropharyngeal and levels II–IV commonly involved.
Post-cricoid region	Anterolaterally: laryngeal invasion (vocal cord fixation). Superiorly: pyriform sinuses. Inferiorly: cricoid cartilage and cervical esophagus. Nodes: commonly levels II–IV and paratracheal nodes.

Important points by subsite

• Pyriform sinuses: Most common hypopharyngeal site (65–85%); visualized endoscopically; lesions may extend inferiorly to the apex at the crico-arytenoid joint forming an inverted cone.
• Posterior pharyngeal wall: Less common; tends to spread superiorly to oropharynx and inferiorly to cervical oesophagus; may involve retropharyngeal space.
• Post-cricoid region: Least common; mucosa spans posterior larynx and may cause early laryngeal invasion; skip metastasis to cervical oesophagus can occur.
• Because hypopharynx is contiguous with larynx and oesophagus, check for involved adjacent structures (laryngeal fixation, oesophageal extension) which influence staging and management.

Clinical and imaging assessment

• Histology: Vast majority are squamous cell carcinomas; variants (verrucous, basaloid, spindle cell) and salivary-type tumours are less common.
• History: Focus on tobacco/alcohol history, otalgia (CN X involvement), respiratory function, voice quality and baseline swallowing function — essential when considering organ preservation.
• Clinical exam: Palpation of base of tongue (for pre-epiglottic involvement), assessment of vocal cord mobility and presence of cervical adenopathy.
• Endoscopic fibre-optic exam: Essential to identify mucosal subsites involved, vocal cord fixation and extent for AJCC staging and treatment decisions. Phonation and Valsalva maneuvers can help visualize hypopharynx.
• Imaging: Contrast-enhanced CT or MRI thin-slice (1–2 mm) dedicated to the larynx/hypopharynx for local extent; attention to pre-epiglottic or paraglottic space, cartilage invasion, oesophageal extension and extracapsular spread.
• PET/CT: Useful for nodal and distant disease, and to delineate borders where metabolic activity clarifies extent; interpret small nodes cautiously.

Setup and imaging protocol

• Position: Simulate patient supine with headrest; the neck should be hyperextended when possible, or use a shoulder pull board to lower shoulders out of beam path.
• Immobilization: Customized 5-point Aquaplast mask to immobilize head, neck and shoulders; consider shoulder pull board for lower neck tumours to remove shoulders from beam path.
• CT simulation: Thin-slice imaging (≤3 mm; 1–2 mm ideal) with IV contrast from skull base to carina to include all nodal drainage stations and potential thoracic spread.
• Isocenter: Typically at center of primary target; for inferiorly-extending lesions place isocenter lower to ensure coverage. Place radiopaque markers for scars or stomas if present.
• MRI and PET fusion: Register MRI and PET to CT simulation dataset. Using the immobilization mask during PET improves fusion accuracy. MRI coil selection may be constrained by the mask.
• IGRT: Daily cone-beam CT aligned to soft-tissue when possible; daily kV imaging matched to bony landmarks and weekly CBCT acceptable depending on departmental workflow.
• Patient instruction: Avoid swallowing during scan acquisition when possible. Consider bolus for anterior mucosal lesions to ensure superficial coverage.

Planning principles and dose concepts

• IMRT planning is recommended. Typical strategy: initial plan (~30 fractions) with dose-painting — e.g., 54 Gy @1.8 Gy/fx to elective/subclinical regions and 60 Gy @2 Gy/fx to higher-risk subclinical regions followed by 10 Gy cone-down to gross disease to a total of 70 Gy over ≈35 fractions. Single dose-painted plans achieving 70 Gy over 33–35 fractions are also acceptable.
• Extended IMRT fields preferred over low anterior neck fields to avoid match-line failures.
• Early-stage disease (T1–T2 N0) often treated definitively with radiation for organ preservation; due to high occult nodal disease, bilateral nodal chains should often be included.
• Advanced disease (≥T3 or node-positive) requires comprehensive coverage; options include definitive chemoradiation, surgery ± adjuvant therapy, or induction chemotherapy followed by local therapy as appropriate.

Suggested target volume definitions (detailed)

Target	Definition / description
GTV 70	All gross primary tumour and involved lymph nodes identified on exam and imaging (CT/MRI/PET). Include nodes ≥1 cm or PET-avid; consider including borderline nodes when in doubt.
CTV 70	Typically equals GTV70 where visualization is clear. If uncertainty exists, add 0–5 mm margin to form CTV70, respecting anatomic barriers.
PTV 70	CTV70 + 3–5 mm depending on immobilization, laryngeal motion and IGRT availability.
CTV 54–60 (subclinical primary/site)	Should encompass entire primary-site GTV and extend to cover the hypopharynx from superior to inferior extents as appropriate, including mucosal/submucosal spread. For subglottic/tracheal extension include level VI/paratracheal nodes.
Elective nodal CTVs	High-risk nodal regions include levels II–IV and retropharyngeal/retrostyloid nodes on involved side; include bilateral necks in many cases. Adjust cranial/caudal extents per node-positive status (e.g., base of skull for level II involvement; include level VI for subglottic disease).
PTV (subclinical)	CTV + 3–5 mm depending on immobilization and IGRT; reduce margins with daily CBCT when feasible.

Dose & fractionation (examples)

• Sequential approach: elective/subclinical 54 Gy @1.8 Gy/fx and 60 Gy @2 Gy/fx to higher-risk subclinical volumes followed by a 10 Gy cone-down to gross disease (total 70 Gy over ~35 fractions).
• SIB/SBRT-style dose-painted IMRT (70 Gy to GTV; 56–60 Gy high-risk subclinical; 50–54 Gy low-risk) is an acceptable alternative depending on concurrent chemotherapy and protocols.

Suggested target volumes for the gross disease region

Target volumes	Definition and description
GTV_70	Primary: all gross disease delineated on CT, MRI, or PET. Lymph nodes: lymph nodes ≥1 cm, or suspicious FDG-avid lymph nodes should be included as nodal GTV.
CTV_70	At MSKCC an additional margin for CTV_70 is not utilized routinely. However, if uncertainty exists regarding extent of disease, a margin can be used. Primary: GTV_70 + 5 mm margin (if used). Lymph nodes: GTV_node + 3 mm margin. (In general GTV_70 = CTV_70 where no additional CTV margin is needed.)
PTV_70	Primary: CTV_70 + 3–5 mm margin (based on comfort with daily imaging and setup error). Lymph nodes: CTV_node + 3–5 mm margin.

Suggested target volumes for the high-risk subclinical region

Target volumes	Definition and description
CTV_60	Primary: GTV_70 with a 1 cm margin + the entire subsite + the larynx (from hyoid to cricoid). Include adjacent mucosal sites at risk for mucosal or submucosal infiltration. Site-specific coverage considerations: Pyriform sinus: include arytenoids, paraglottic space, thyroid cartilage for laterally involved lesions, constrictor muscles or prevertebral muscle for posterior involvement, pre-epiglottic space or structures in oropharynx for superior extension, and post-cricoid area for inferior lesions. Posterior pharyngeal wall: include pre-vertebral fascia and retropharyngeal space; consider adjacent oropharynx if superior extension and proximal cervical esophagus if inferior extension. Post-cricoid region: consider coverage of pyriform sinuses for superior-extending lesions, cover cricoid cartilage if involved, and proximal cervical esophagus if inferior extension present. Lymph nodes: Any lymph nodes in CTV_70 should be included. In ipsilateral or node-positive necks include lateral retropharyngeal lymph nodes (start at skull base at entrance of carotid canal), II–IV (include retrostyloid space for superior level II). For inferior hypopharyngeal tumours, pyriform sinus tumours involving the apex, and advanced T-stage — consider level VI coverage. For midline post-cricoid and posterior pharyngeal wall tumours with involved nodes consider bilateral lateral retropharyngeal, II–IV and VI coverage. For inferior tumours consider paratracheal and superior mediastinal nodes. Retropharyngeal node coverage in node-positive necks is recommended. Consider ipsilateral level IB if level II is involved. If posterior level II–IV nodes are involved consider covering level V.
PTV_60	CTV_60 + 3–5 mm margin depending on comfort with daily target localization (reduce margins with daily IGRT).
Post-operative cases: Include the entire surgical bed and bilateral dissected neck inclusive of clips and wired scars. Areas at risk for positive margin or ECE should be delineated in conjunction with the surgeon and may be treated to 66 Gy.

Suggested target volumes for the low-risk subclinical region

Target volumes	Definition and description
CTV_54	Contralateral or node-negative neck: include lateral retropharyngeal lymph nodes (can start at C1 vertebral body), levels II–IV. Level II superior border can start where posterior belly of digastric crosses internal jugular vein. Exception: in midline hypopharyngeal tumours with bilateral retropharyngeal involvement, include contralateral retropharyngeal nodes. In midline tumours that are node-positive, the contralateral neck is also considered high risk.
PTV_54	CTV_54 + 3–5 mm margin depending on comfort with daily target localization and IGRT.
Note: Dose suggestions — 70 Gy prescribed in 2 Gy fractions for gross disease; if using 70/60/54 for gross, high-risk and low-risk subclinical regions respectively, one can plan a SIB or a sequential technique (e.g., single 10 Gy cone down to PTV_70). Adjust fractionation per institutional protocol.