LARYNX-TARGET VOLUME DELINEATION

Key anatomy & spread patterns

• The larynx is divided into three subsites: supraglottis, glottis and subglottis.
• The supraglottic larynx includes the ventricles, false vocal cords (FVC), arytenoids, aryepiglottic folds and epiglottis (suprahyroid, infrahyoid, laryngeal surface).
• Bilateral elective nodal irradiation is generally warranted for supraglottic tumours due to rich lymphatic drainage.
• The glottic larynx includes the true vocal cords (TVC), anterior & posterior commissures and the infraglottic space (~0.5 cm inferior to the free margin of the true vocal cords).
• Early-stage glottic tumours (T1–T2 N0) often do not require elective nodal irradiation; mobility of the TVC must be assessed (normal, hypomobile, fixed) because fixation suggests recurrent nerve injury or muscle invasion.
• Subglottic larynx extends from the inferior border of the glottis to the superior border of the trachea — bilateral level VI coverage is recommended for subglottic involvement given the propensity for nodal spread.
• Thyroid cartilage invasion: inner cortex invasion = T3 disease, outer cortex invasion = T4 disease; imaging (CT/MRI) is required to assess degree of invasion. For true T4 disease, total laryngectomy is often preferred; organ preservation considered selectly.

Recommended assessments

• Comprehensive physical examination with laryngoscopy (direct or flexible) to assess mucosal extent and TVC mobility.
• High-resolution, thin-slice (1–2 mm) CT and/or MRI of the larynx with IV contrast for local extent evaluation; careful attention to pre-epiglottic and paraglottic spaces and thyroid cartilage invasion.
• Contrast-enhanced MRI helpful for locoregional soft tissue definition; note that >1 cm base of tongue invasion was an exclusion criterion in some larynx preservation trials.
• PET/CT useful for nodal and distant disease evaluation but may miss small-volume nodal disease — interpret negatives cautiously.
• Document any subglottic, pre-epiglottic or paraglottic extension as these may change staging and treatment approach.

Simulation protocol — practical points

• Position: Supine with headrest and neck extended in a reproducible position.
• Immobilization: Use a five-point customized Aquaplast mask immobilizing head, neck and shoulders. A shoulder pull board can lower the shoulders out of the beam path.
• For dental metal, consider a custom mouthguard to reduce electron scatter and mucositis risk.
• CT simulation: ≤3 mm slice thickness with IV contrast; include the entire vertex through the carina.
• Isocenter: Typically placed at the arytenoids; if subglottic or hypopharyngeal extension present, place isocenter 1 cm inferiorly.
• Postoperative: place a radiopaque marker on the scar to guide contouring and matching.
• IGRT approaches: daily CBCT aligned to the larynx is ideal; daily kV imaging aligned to bone and weekly CBCTs are alternatives. Orthogonal kV systems or MV CT (TomoTherapy) are acceptable when available.
• Instruct patients not to swallow during simulation/IGRT when feasible. Use bolus to ensure anterior coverage for tumours involving the anterior commissure.

Principles & definitions

• The GTV must be delineated using all available clinical information: laryngoscopy (direct/flexible), CT, MRI and PET. Document which modalities were used for each GTV contour.
• Define positive lymph nodes as those with central necrosis, extracapsular extension (ECE), and/or a short-axis diameter >1 cm. Nodes with FDG avidity on PET should be considered malignant even if small.
• Small, bean-shaped nodes or nodes with a fatty hilum are more likely benign, but enlarged RP nodes should still be considered suspicious in laryngeal cancer.
• When in doubt, include borderline nodes as GTV to avoid undertreatment; clearly document rationale in the plan note.
• Suggested target volumes and margins are summarized below (Tables 4.1–4.3 derived from the provided guidance).

Suggested target volumes for gross disease (locally advanced glottic, supraglottic, or subglottic laryngeal cancers)

Target volumes	Definition and description
GTV 70	Primary: all gross disease identified on physical examination and imaging (CT/MRI/PET). Neck nodes: all nodes ≥1 cm or PET-positive should be included as nodal GTV. Include borderline lymph nodes as GTV when in doubt to avoid undertreatment.
CTV 70	Usually the same as GTV70 (no additional margin) when visualization is excellent. If uncertainty exists about extent of gross disease, consider adding an additional 0–5 mm margin to create CTV70.
PTV 70	CTV70 + 3–5 mm, depending on reproducibility of daily patient positioning and available IGRT.

Suggested target volumes for subclinical disease (supraglottic, subglottic, or locally advanced glottic cancers)

Target volumes	Definition and description
CTV 54–60	CTV 54–60 should encompass the entire GTV and the primary-site CTV should include the entire larynx from the bottom of the hyoid (or top of the thyroid notch) to the bottom of the cricoid cartilage; extend inferiorly when necessary for subglottic disease.
High-risk nodal regions	Include levels II–IV and the retrostyloid/retropharyngeal space on the involved side. In the node-positive neck, level II should be treated to the base of skull and ipsilateral retrostyloid nodes included. Level VI should be included if there is subglottic extension or tracheal involvement.
Level selection and boundaries	In the node-negative neck, the superior border of level II commonly stops where the posterior belly of the digastric crosses the internal jugular vein (caudal edge of the lateral process of C1). Level IB and V are not routinely included unless gross disease exists at those levels. RP nodes may be included at physician discretion for bulky adenopathy. Level VII coverage is recommended for subglottic extension or hypopharyngeal involvement.
PTV 54–60 / PTV 54	PTV = corresponding CTV + 3–5 mm depending on immobilization, localization and IGRT. Reduce margins when robust immobilization and daily CBCT is used.
Subclinical dose recommendations	High-risk subclinical dose: ~1.8–2 Gy per fraction to reach 54–60 Gy. Low-risk subclinical dose: ~1.54–1.8 Gy per fraction to 54 Gy (various fractionation patterns exist; choose according to protocol).

Suggested target volumes for postoperative laryngeal cases

Target volumes	Definition and description
CTV 60	CTV 60 should encompass the entire operative bed, the scar, any stoma, and the node-positive neck (levels II–IV, the retrostyloid space and involved nodal stations). This is the high-risk postoperative volume.
CTV 54	The node-negative neck: include levels VI and VII when there is subglottic extension or a stoma. Treat levels II–IV for elective coverage depending on primary site and pathology.
CTV 66	Areas of positive margins, extracapsular extension (ECE), or a stoma boost if indicated — CTV 66 may be delivered with a sequential cone-down or dose painting technique.
PTV	PTV = CTV + 3–5 mm, depending on immobilization, IGRT and reproducibility.

Additional practical points

• Always include pre-treatment imaging when planning after induction chemotherapy — fuse pre-chemo studies to the planning CT and include the pre-chemo extent in the high-risk CTV (modified for anatomic changes and natural barriers).
• Use a conservative approach for margins near critical structures and when imaging is uncertain — multidisciplinary discussion is recommended for borderline cases.
• Document clearly in the plan note: imaging used for contouring, margins applied, levels included, and rationale for elective coverage (unilateral vs bilateral neck treatment).

Recommended CTV coverage and technical considerations

• CTV should encompass the entire larynx including anterior & posterior commissures and arytenoids.
• Coverage guidance: from bottom of thyroid notch superiorly to cricoid cartilage inferiorly for T1; extend to first tracheal ring for T2 when needed.
• Ensure adequate inferior coverage — many recurrences occur inferiorly.
• Consider ipsilateral cord sparing in selected unilateral lesions.
• Radiation dose examples: for T1 glottic tumours, a regimen like 63 Gy in 28 fractions (≈2.25 Gy/fx) has evidence supporting local control; for T2N0, higher doses (>65 Gy) with dose per fraction ≥2.25 Gy may improve local control (selected regimens cited in literature).

Strategy and fractionation considerations

• Include bilateral necks for most advanced cases.
• Sequential cone-down approach: initial phase treats subclinical regions and lower risk areas followed by cone-down to gross disease to reach ~70 Gy total (examples: initial 54 Gy to elective and 60 Gy to low/high risk subclinical followed by 10 Gy cone-down to gross disease).
• SIB and dose-painted IMRT options are acceptable; choose schedules compatible with concurrent systemic therapy when used.
• Subclinical primary-site CTV must encompass entire larynx from bottom of thyroid notch to first tracheal ring or extend inferiorly when indicated.
• Subclinical nodal CTV should include at least levels II–IV and often level VI depending on tumor site and subglottic involvement; adjust cranial extent in node-positive necks to include base of skull/retrostyloid nodes.

Indications & recommended volumes (detailed)

• Adverse pathologic features warranting postoperative radiation (per NCCN v2020): positive margins, close margins, extracapsular extension (ECE), pT4 primary, pN2–pN3 nodal disease, perineural invasion, vascular invasion, lymphatic invasion.
• Concurrent chemotherapy should be added for extracapsular extension or positive margin.

Target volume	Definition & recommended dose/notes
High-risk CTV (eg CTV 60)	The entire surgical bed, stoma, scar and the dissected node-positive neck should be included in a high-risk CTV to a dose of ~60 Gy. Areas of positive margin or extracapsular extension may be boosted to 66 Gy (consider sequential cone-down or dose painting).
Low-risk CTV (eg CTV 54)	The undissected node-negative neck can be included in the low-risk CTV to ~54 Gy. Levels included depend on primary site and intraoperative findings (e.g., include levels VI/VII when subglottic involvement or stoma present).
Stoma boost	The stoma may be boosted to 66 Gy for subglottic extension or if an emergent tracheostomy was performed; consider anatomy as a tracheoesophageal node risk.
PTV	PTV = CTV + 3–5 mm depending on immobilization, IGRT and reproducibility.

• Subclinical disease can be contoured as one or two CTVs (high-risk & low-risk) with typical subclinical doses of 1.8–2 Gy per fraction to achieve 54–60 Gy.
• Areas requiring boost (positive margins/ECE) often receive ~66 Gy (sequential cone-down or dose painting).

Key principles

• Fuse pre-chemotherapy imaging (baseline) with planning CT to guide target delineation post-induction; the pre-chemotherapy extent of disease should inform the high-risk subclinical volume.
• The pre-chemotherapy CTV should be modified for anatomic changes after chemotherapy and should exclude natural barriers (air, bone) to spread; account for tumor shrinkage and displacement but preserve coverage for sites at risk for microscopic disease.

Planning considerations

• Use a PTV margin of approximately 0.3–0.5 cm (3–5 mm) depending on immobilization and laryngeal motion — smaller margins may be used with highly reproducible immobilization and daily IGRT.
• For tumours involving the anterior commissure, use flash and bolus to ensure adequate coverage of superficial extents of gross or subclinical disease.
• Limit dose heterogeneity: plan to keep hot spots below ~105% of the prescription when treating the larynx to avoid focal overdose to cartilage and mucosa.
• Document the pre-chemotherapy extent and rationale for modified CTVs in the plan note; reconcile differences between pre- and post-chemo imaging with multidisciplinary input.