TARGET VOLUME DELINEATION IN RADIATION ONCOLOGY

General Principles of Planning & Target Delineation

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Key points

  • Perform comprehensive oral examination, biopsy and dedicated imaging for staging and planning.
  • CT is commonly used to evaluate local extent and nodal spread; MRI provides superior soft-tissue resolution for perineural spread and deep tissue involvement. PET/CT is useful for identifying regional nodal disease and distant metastases.
  • Clinical target volumes in definitive settings typically include GTV70 (all known gross disease) and are often similar to CTV70. In practice define GTV precisely and add margins for microscopic disease as per tables below.
  • In postoperative setting, define high-risk (CTV66), intermediate-risk (CTV60) and low-risk (CTV54) CTVs according to pathology and preoperative extent.
Document imaging modalities used and the rationale for margins and nodal coverage in the plan note.

CT Simulation & Immobilization

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Simulation checklist

  • Use CT simulation with IV contrast (thin slice). Include skull base to thoracic inlet as needed for nodal coverage.
  • Use a bite block to depress the tongue and protrude the lower lip and/or to elevate the hard palate when applicable to improve reproducibility.
  • For patients with scar risk or extramucosal extension, consider tissue-equivalent bolus. Wire any surgical scars or drain sites for postoperative cases.
  • Immobilize supine with neck slightly hyperextended using a five-point thermoplastic mask for head & neck control.
Record bite block, bolus, wire/scar placements and immobilization details in the simulation note for daily reproducibility.

Target Volume Delineation & Treatment Planning

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Principles

  • GTV: delineate all gross tumour and involved nodes using CT/MRI/PET and clinical/endoscopic information.
  • CTV70 (definitive): usually the GTV70 itself; if uncertainty exists add a small margin (e.g., 5 mm) excluding bone and air where appropriate.
  • In postoperative setting: CTV66 targets areas of soft tissue/bone invasion or microscopically positive margins; CTV60 includes preoperative gross disease and operative bed.
  • CTV54 (low-risk): ipsilateral or contralateral uninvolved nodal levels at low risk for subclinical disease (site-specific guidance in Table 6.3).
  • PTV margins: commonly 3–5 mm added to CTV depending on immobilization, daily IGRT and institutional practice (reduce margins with robust IGRT).
In definitive cases, plan should make GTV70 and CTV70 explicit, and specify any additional margins used for CTV or PTV.

Suggested Target Volumes & Dosing

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Suggested target volumes for definitive treatment

TargetDefinition & notes
GTV70Primary: all gross disease on physical examination and imaging. Neck nodes: all gross disease on exam and imaging.
CTV70Same as GTV70, although a 5 mm margin (excluding bone) may be added if uncertainty exists regarding full extent of gross disease.
CTV59.4Primary: encompass entire CTV70 and the entire anatomic subsite (e.g., oral tongue entire subsite if primary). Include subclinical mucosal target volume per site-specific recommendations.
CTV54Neck nodes: nodal levels with pathologic involvement and adjacent ipsilateral or contralateral nodal regions at high risk for subclinical disease (site-specific per Table 6.3).
PTV (general)PTV70 is typically ~69.96 Gy in 2.12 Gy fractions (or 70 Gy in 2 Gy fractions); PTV59.4/PTV54 depending on fractionation chosen. Standard PTV margins: CTV + 3–5 mm.

Suggested targets & dosing for postoperative treatment

TargetDefinition & notes
CTV66Primary: regions of soft tissue/bone invasion or microscopically positive margins if present. Neck nodes: regions of extracapsular extension if present.
CTV60Primary: preoperative gross disease and the entire tumor bed and anatomic subsite. Neck nodes: preoperative gross disease, operative bed, and ipsilateral/contralateral nodal regions at high risk for subclinical disease.
CTV54Ipsilateral and/or contralateral uninvolved nodal levels at low risk for subclinical disease (site-specific recommendations given in Table 6.3).
PTVPTV margins generally CTV + 3–5 mm depending on immobilization and IGRT. Typical suggested doses: PTV70 ≈70 Gy (definitive), PTV59.4 ≈59.4 Gy or PTV54 ≈54 Gy for subclinical regions depending on fractionation.
Subscript numbers in tables reflect suggested prescription doses. Adjust fractionation per institutional protocols and patient factors.

Site-specific guidelines (oral cavity)

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Overview — how to apply site specifics

Tumour site & stageHigh-risk clinical target (CTV59.4a or CTV60)Low-risk clinical target (CTV54)
Oral tongue, floor of mouth — T1–T4N0 Tumor bed, entire oral tongue or involved portion, base of tongue where applicable; include bilateral levels I–IV at physician discretion. Bilateral levels I–IV at clinician discretion regarding inclusion in high- vs low-risk targets; prophylactic level VI when indicated.
T1–T4N1–3 (oral tongue) As above but include level VI nodal regions when indicated or high-risk features present. Same as above except include level VI when indicated.
Buccal mucosa, retromolar trigone, hard palate, gingiva — T1–T2N0 Tumor bed and ipsilateral levels I–IV at physician's discretion. Ipsilateral lymph nodes levels I–IV as per clinician discretion.
T3–T4N0 (buccal, gingiva, retromolar trigone) Tumor bed and ipsilateral levels I–IV (or bilateral levels I–V if contralateral nodes involved). Contralateral lymph nodes levels II–IVc if contralateral nodes are uninvolved (consider omission of contralateral neck in well-lateralized small tumors per clinician).
These are concise summaries — follow the full site-specific table for detailed decisions (e.g., when to include level VI, when contralateral coverage required). Use pathology, imaging and multidisciplinary input to finalize volumes.