In oral cavity cancer, target volume delineation has to follow the involved subsite, the presence of bony invasion, and the nodal drainage pattern of each primary. For a broader view of the topic, see the Target Volume Delineation and Field Setup – Complete Clinical Guide; this detailed article stays with the oral cavity chapter and focuses on clinical target volumes, dose levels, and setup details.
The chapter takes a practical line from the start. Coverage does not stop at the visible lesion. It expands to the whole anatomic subsite when that is needed to address subclinical spread, and it reshapes the neck volume according to the behavior of each oral cavity site. For comparison with another head and neck primary, it is useful to review our article on oropharyngeal carcinoma target delineation.
General principles of planning and target delineation
The recommended workup begins with a comprehensive oral examination, biopsy, and imaging for staging and treatment planning. Computed tomography is commonly used to define the local extent of disease and regional spread to cervical lymph nodes. In the oral cavity, the book specifically points to CT as a strong tool when the question is invasion of the mandible, maxilla, or pterygopalatine fossa.
MRI becomes more useful when the target depends on soft tissue extension or perineural spread, because the chapter describes it as superior to CT for both. PET is helpful for regional nodal involvement and distant disease. That combination matters in practice: the imaging choice does not just document stage, it changes where the clinical target volume should begin and end.
CT simulation and setup details
The simulation recommendation is CT with intravenous contrast. A bite block may be used during simulation and throughout treatment to depress the tongue, protrude the lower lip, and elevate the hard palate. Those are small setup moves, but they change the geometry of the oral cavity and can make target coverage more reliable.
When extranodal extension is present, or when the surgical scar is at risk, the chapter recommends tissue-equivalent skin bolus. Surgical scars and drain sites should be wired. The patient is immobilized supine with the neck slightly hyperextended in a five-point thermoplastic mask. Across the clinical examples, bolus and flash return whenever there is concern for soft tissue involvement or superficial coverage.
Oral cavity cancer target delineation for definitive treatment
For definitive treatment, the chapter divides the clinical target into three risk layers. GTV70 contains all gross disease on physical examination and imaging in both the primary and the neck. CTV70 is usually the same as GTV70, although a 5 mm margin excluding bone may be added if the full extent of gross disease is uncertain. CTV59.4 then expands to the entire anatomic subsite and to high-risk nodal regions, while CTV54 covers lower-risk elective nodal levels.
That structure prevents a common planning mistake: using a uniform shell around the gross tumor and assuming that the subclinical problem is solved. In oral tongue disease, the whole oral tongue belongs in the subclinical target. In buccal mucosa tumors, the entire buccal mucosa belongs there. The chapter treats that as an anatomic rule rather than a stylistic preference.
Table 6.1. Suggested target volumes and dose levels for definitive treatment
The table below summarizes the proposed target hierarchy for definitive treatment. The key distinction is between gross disease, the full anatomic subsite at risk, and uninvolved nodal levels that still require elective coverage.
| Target volume | Definition and description |
|---|---|
| GTV70 | Primary: all gross disease on physical examination and imaging. Neck nodes: all gross disease on physical examination and imaging. |
| CTV70 | Same as GTV70, although a 5 mm margin excluding bone may be added when there is uncertainty about the full extent of gross disease. |
| CTV59.4 | Primary: encompass the entire CTV70 and the entire anatomic subsite; if the disease is in the oral tongue, the entire oral tongue should be included in the subclinical target volume; if it is a buccal mucosa tumor, the entire buccal mucosa should be included. Neck nodes: nodal levels with pathologic involvement and adjacent ipsilateral or contralateral nodal regions at high risk for subclinical disease, with site-specific recommendations in Table 6.3. |
| CTV54 | Ipsilateral and/or contralateral uninvolved nodal levels at low risk for subclinical disease, with site-specific recommendations in Table 6.3. |
The subscript numbers represent suggested prescribed doses. PTV70 is 69.96 Gy in 2.12 Gy per fraction, PTV59.4 is 59.4 Gy in 1.8 Gy per fraction, and PTV54 is 54 Gy in 1.64 Gy per fraction; alternative fractionations are 70 Gy in 2 Gy per fraction delivered with sequential or simultaneous integrated boost techniques.
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 6.1)
Postoperative oral cavity cancer target delineation
Postoperative planning shifts the emphasis from visible disease to the full operative bed, microscopic risk, and extranodal extension. CTV66 includes regions of soft tissue or bone invasion and microscopically positive margins when present. In the neck, it covers regions of extracapsular extension when present.
CTV60 includes preoperative gross disease, the entire tumor bed, and the relevant anatomic subsite. In the neck, it includes the preoperative gross disease, the entire operative bed, and ipsilateral or contralateral nodal regions at high risk for subclinical spread. CTV54 covers lower-risk uninvolved nodal levels. If gross residual disease remains, the chapter states that a GTV should also be contoured.
Table 6.2. Suggested target volumes and dose levels for postoperative treatment
This table is useful when the practical question is where the operative bed stops and where elective neck coverage begins. It also clarifies when dose escalation follows positive margins or extranodal extension.
| Target volume | Definition and description |
|---|---|
| CTV66 | Primary: regions of soft tissue or bone invasion, or microscopically positive margins, if present. Neck nodes: regions of extracapsular extension, if present. |
| CTV60 | Primary: preoperative gross disease, the entire tumor bed, and the entire relevant anatomic subsite. Neck nodes: preoperative gross disease, the entire operative bed, and ipsilateral or contralateral nodal regions at high risk for subclinical disease, with site-specific recommendations in Table 6.3. |
| CTV54 | Ipsilateral and/or contralateral uninvolved nodal levels at low risk for subclinical disease, with site-specific recommendations in Table 6.3. |
The subscript numbers represent suggested prescribed doses. PTV66 is 66 Gy in 2.2-2.0 Gy per fraction, PTV60 is 60 Gy in 2 Gy per fraction, and PTV54 is 54 Gy in 1.8 Gy per fraction.
If gross residual disease is present, a GTV should be delineated.
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 6.2)
Site-specific oral cavity guidelines
Table 6.3 is the most practical part of the chapter for elective neck design. In oral tongue and floor of mouth T1-T4N0 disease, the high-risk volume includes the tumor bed, the entire oral tongue, the base of tongue, and bilateral levels I-IV, with physician discretion regarding which levels remain in the high-risk or low-risk compartment. When the stage is N1-N3, that same logic extends to level VI. The text is explicit that level VI is a drainage site for oral tongue cancer, often in node-positive patients, and strongly recommends including it in the target.
The figure captions sharpen that guidance. Level IA should be covered for oral tongue primaries. Level V coverage is recommended for oral tongue, especially after neck surgery and in the presence of ipsilateral nodal disease. The retropharyngeal nodes are described as low risk and are not included, while the ipsilateral retrostyloid space is at risk for nodal metastasis, particularly with level II involvement.
For buccal mucosa, retromolar trigone, hard palate, and gingiva, the design changes with stage and laterality. T1-T2N0 disease allows the tumor bed and ipsilateral levels I-IV at physician discretion. In T3-T4N0 disease, the table keeps ipsilateral levels I-IV in the high-risk target and adds contralateral levels II-IV as low-risk nodal coverage. In N1-N3 disease, the high-risk volume includes the tumor bed and ipsilateral levels I-V, or bilateral levels I-V if contralateral nodes are involved, while the low-risk volume includes contralateral levels II-IV if they are uninvolved. For well-lateralized buccal mucosa, gingiva, or retromolar trigone tumors, the contralateral neck may be omitted at the treating physician’s discretion. For hard palate tumors, which are typically salivary in origin such as adenoid cystic carcinoma, the track of the trigeminal nerves should be covered and the neck may be omitted because nodal spread is low.
Table 6.3. Site-specific clinical target guidelines
This table condenses the differences between oral tongue, floor of mouth, buccal mucosa, retromolar trigone, hard palate, and gingiva. Several entries deliberately leave room for physician judgment rather than assigning every nodal level automatically.
| Tumor site | Stage | High-risk clinical target volume (CTV59.4 or CTV60)a | Low-risk clinical target volume (CTV54) |
|---|---|---|---|
| Oral tongue, floor of mouth | T1-T4N0 | Tumor bed, entire oral tongue, base of tongue, and bilateral levels I-IV, with physician discretion regarding whether some levels should be in the high-risk or low-risk target volumeb. | Bilateral levels I-IV, with physician discretion regarding whether some levels should be in the high-risk or low-risk target volumeb. Prophylactic coverage of level VI when indicated. |
| Oral tongue, floor of mouth | T1-T4N1-3 | Same as above, except to also include level VI nodal regions. | Same as above, except to also include level VI nodal regions. |
| Buccal mucosa, retromolar trigone, hard palate, gingiva | T1-T2N0 | Tumor bed and ipsilateral levels I-IV at physician discretionb. | Ipsilateral lymph node levels I-IV at physician discretionb. |
| Buccal mucosa, retromolar trigone, hard palate, gingiva | T3-T4N0 | Tumor bed and ipsilateral levels I-IV. | Contralateral lymph node levels II-IVc. |
| Buccal mucosa, retromolar trigone, hard palate, gingiva | T1-T4N1-3 | Tumor bed and ipsilateral levels I-V, or bilateral levels I-V if contralateral involved nodes are presentc. | Contralateral lymph node levels II-IVc if uninvolved. |
a 66 Gy for microscopically positive margins or extracapsular extension; 70 Gy if gross residual disease is present.
b The decision to place a level in the high-risk or low-risk region depends on other tumor features and physician discretion. Level VI is a drainage site for oral tongue cancer, often in node-positive disease. The chapter strongly recommends including it in the target.
c For well-lateralized buccal mucosa, gingiva, and retromolar trigone cancers, treatment of the contralateral neck can be omitted at the treating physician’s discretion. Hard palate tumors are typically salivary in origin, such as adenoid cystic carcinoma, and coverage of the trigeminal nerve pathway should be included. Because these tumors have low nodal spread, the neck may be omitted.
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 6.3)
Clinical figures from the chapter
The figures show what that planning logic looks like on real axial slices. In the gingival squamous cell carcinoma example, pathologic stage T4aN1 with bone invasion, Figure 6.4 places CTV66 across the region of bony invasion, CTV60 across the full operative bed and ipsilateral neck levels I-IV, and CTV54 across contralateral neck levels I-IV. The chapter justifies the contralateral low-risk neck by the combination of node-positive disease and T4 stage.
Figure 6.5 moves to buccal mucosa disease, pathologic stage T2N3b, after resection and right neck dissection with extranodal extension at level IB and a negative but close deep margin. CTV66 covers the nodal region with extranodal extension. CTV60 includes the operative bed and the entire buccal mucosa, extending cranially to the buccal-gingival sulcus and infratemporal fossa at the inferior orbital rim, caudally to the buccal-gingival sulcus and submandibular gland, anteriorly at least to the lip commissure, and posteriorly to the retromolar trigone. The chapter recommends wide margins even for smaller primaries and places skin bolus to cover the high- and intermediate-risk targets. CTV54 includes contralateral levels I-III because of the extent of ipsilateral nodal disease.
Figure 6.6 applies the same framework to floor of mouth squamous cell carcinoma, pathologic stage T4aN2b with mandibular invasion after right hemimandibulectomy and bilateral neck treatment. CTV66 marks the extensive bony invasion. CTV60 includes the entire operative bed, ipsilateral levels I-V, and the whole floor of mouth complex. The ipsilateral retrostyloid space is also included, especially with level II involvement. CTV54 covers contralateral levels I-IV.
The remaining examples keep the same message consistent. In the postoperative oral tongue case with microscopically positive margins, the chapter recommends ipsilateral levels I-V, contralateral levels I-IV, level IA, and consideration of level VI. In the retromolar trigone case with medial pterygoid involvement, the pterygopalatine fossa should be covered because it is a gateway to the middle cranial fossa. In the postoperative setting overall, the tumor bed volume should follow the entire operative bed, including visible inflammation and edema on the planning CT.
