Lung cancer target volume delineation depends on three decisions the chapter keeps tightly linked: respiratory motion management, accurate reading of thoracic nodal stations, and disciplined margins between GTV, iGTV, iCTV, ITV, and PTV. In both NSCLC and SCLC, CT-based planning with conformal techniques remains the standard of care, but high conformity is only useful when the gross disease, the mobile component, and the nearby organs at risk have been drawn correctly.
3D-CRT, IMRT, and SBRT all use multiple beam angles, yet they do not forgive poor contouring. If the target is wrong, the DVH simply reports the mistake in a polished way. That is why the chapter anchors planning in physical examination, contrast-enhanced CT, PET, and mediastinal assessment with mediastinoscopy or EBUS before the final field design is locked in. For the broader framework, read our complete guide to target volume delineation and field setup. If you want to compare how the same contouring discipline applies in another disease site, see our dedicated article on larynx cancer delineation.
In this article
- Planning principles in lung cancer
- Mediastinal nodal stations and risk patterns
- How to build GTV, iGTV, iCTV, ITV, and PTV
- Early-stage NSCLC: SBRT, the PBT, and the no-fly zone
- Stage II-III NSCLC: margins and dose
- Postoperative NSCLC
- SCLC and consolidative thoracic radiotherapy
- Accepted dose regimens
- When CBCT changes the plan
- References
Planning principles in lung cancer
In lung cancer, CT-based planning and respiratory motion management are the standard of care for both NSCLC and SCLC. The chapter does not frame simulation, positioning, and immobilization as setup trivia. They determine how many beam arrangements are genuinely usable and how safely the team can reduce margins.
Patients should ideally be simulated with the arms above the head to maximize beam geometry options. A four-dimensional simulation should be performed to assess internal motion. In thoracic radiotherapy that decision has direct downstream effects, because it shapes whether the team builds an iGTV-first workflow or relies on an ITV after CTV expansion.
The chapter is equally explicit about nearby normal structures. When they are close to the treatment field, the heart, lungs, spinal cord, esophagus, chest wall, great vessels, proximal bronchial tree, and brachial plexus should be contoured. For superior tumors, or for high paratracheal and supraclavicular nodal disease, the brachial plexus becomes especially important. The liver should be contoured for right lower lobe disease near the diaphragm, and the spleen can become dosimetrically relevant in very low left lower lobe tumors or left pleural tumors.
Field design is then narrowed by the chapter’s clear preference for involved-field treatment. In gross NSCLC and SCLC, prior series showed low failure rates in elective nodal regions, and a randomized trial favored involved-field over elective nodal irradiation. The practical message is that elective nodal coverage should not be routine when the treating physician is confident about the true extent of active disease.
Mediastinal nodal stations and risk patterns
Involved-field radiotherapy only works when the mediastinal map is second nature. The chapter points readers back to consensus atlases and organizes the stations in a practical way: station 1 in the supraclavicular zone; 2R, 2L, 3a, 3p, 4R, and 4L in the superior mediastinum; 5 and 6 in the aortic region; 7, 8, and 9 in the inferior mediastinum; and N1 stations 10 through 14 across hilar, interlobar, lobar, segmental, and subsegmental anatomy.
That map is more than nomenclature. It drives PET/CT interpretation, EBUS sampling strategy, and the confidence to omit uninvolved nodal regions. Figure 13.1(b) is especially useful because it shows how strongly nodal risk depends on primary tumor location. Right upper lobe tumors favor paratracheal and station 3 involvement, left upper lobe tumors shift risk toward stations 5 and 6, and left lower lobe tumors show a heavier pattern in stations 8 and 7 than in the superior mediastinum.
Risk of nodal involvement by primary tumor location
The table below reproduces the percentages shown in Figure 13.1(b). It is a practical reminder that a limited field is only as safe as the physician’s understanding of lobe-specific drainage.
| Involved station | Right upper lobe (n=45) | Right middle/lower lobe (n=36) | Left upper lobe (n=35) | Left lower lobe (n=8) |
|---|---|---|---|---|
| Upper mediastinum (1) | 9% | 3% | 0% | 0% |
| Paratracheal (2) | 40% | 31% | 3% | 0% |
| Prevascular, retrotracheal, pretracheal (3) | 73% | 47% | 29% | 0% |
| Lower paratracheal (4) | 36% | 28% | 17% | 13% |
| Subaortic (5) | – | – | 71% | 13% |
| Para-aortic (6) | – | – | 43% | 25% |
| Subcarinal (7) | 36% | 69% | 20% | 38% |
| Paraesophageal (8) | 9% | 11% | 3% | 50% |
| Pulmonary ligament (9) | 2% | 6% | 6% | 13% |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Fig. 13.1b)
How to build GTV, iGTV, iCTV, ITV, and PTV
The chapter accepts two coherent ways to build the target. In the first, the physician contours the GTV, measures internal motion, creates the iGTV, expands to iCTV, and then expands again to PTV. In the second, the GTV expands to CTV, the CTV expands to ITV to account for internal motion, and the ITV then expands to PTV. That second pathway also applies after surgery, when there is no macroscopic GTV.
The chapter’s locally advanced NSCLC example is a good illustration of why those definitions matter. The patient had a 2.3 cm right upper lobe tumor with right hilar, subcarinal, precarinal, paratracheal, and right supraclavicular adenopathy. Lung windows on CT were used to delineate the primary tumor and hilar component, while nodal stations were defined through PET/CT, contrast-enhanced CT, and EBUS. That sequence avoids both undercalling the primary lesion and padding the mediastinum without evidence.
The continuation figure shows a planning detail that often separates careful contouring from automatic expansion. The iCTV was edited to exclude bone and esophagus, and the iGTV already accounted for lymph node motion. The margin from iGTV to iCTV was 0.7 cm, followed by 0.5 cm from iCTV to PTV. The chapter is effectively reminding the reader that a clinical target remains a clinical construct, not a geometric halo.
That point becomes even more valuable in the thorax because every unnecessary millimeter can increase dose to lung, esophagus, or central airways. The text never argues for the smallest possible margins at any cost. It argues for margins that match what the imaging and motion assessment genuinely support.
Early-stage NSCLC: SBRT, the PBT, and the no-fly zone
In early-stage NSCLC, margins are intentionally tight because the goal is ablative treatment with high conformity. The chapter gives a standard iGTV-to-iCTV expansion of 0 to 0.2 cm. That small increment makes sense only when motion has already been characterized and the team respects the central thoracic anatomy.
The proximal bronchial tree should be contoured consistently. It includes the distal 2 cm of the trachea, the carina, the right and left mainstem bronchi, and the lobar bronchi. The authors define a radial 2 cm margin beyond the PBT as the no-fly zone. That concept is clinically useful because it separates peripheral lesions from lesions approaching or encroaching on central airways.
The figure set makes the dose logic tangible. A peripheral stage I lesion was treated with 54 Gy in three 18 Gy fractions. A lesion approaching the pulmonary tree in a medically inoperable patient received 48 Gy in four 12 Gy fractions. A central lesion encroaching on the bronchi received 50 Gy in five fractions, and the authors report that they generally constrain the maximum point dose to the PBT to 55 Gy. Across those schedules, the biological objective is consistent: achieve a BED greater than 100 Gy.
That flexibility is one of the strongest practical points in the chapter. Rather than forcing one schedule on every stage I lesion, the authors let dose selection follow location and extent. In real planning work, that is usually safer than treating a peripheral lesion and a central lesion as if the airway anatomy were interchangeable.
Stage II-III NSCLC: margins and dose
For stage II-III NSCLC, the iGTV-to-iCTV margin is typically 0.5 to 0.8 cm, based on prior histologic analyses of microscopic extension. The chapter is even more helpful when it turns to PTV design: 1.0 to 1.5 cm if there is no internal motion assessment or daily image guidance, 0.5 to 1.0 cm if either 4D CT or CBCT is available but not both, and 0.3 to 0.5 cm from CTV, or from iGTV, to PTV when 4D CT planning is combined with kV or CBCT guidance. That last combination is the preferred one.
The clinical examples show why those tiers matter. In the stage IIIB case, the patient received 60 Gy in 30 fractions with separate contours for the primary tumor, nodal disease, iGTV, iCTV, PTV, brachial plexus, and esophagus. In the stage IIIC adenocarcinoma example, the patient presented with superior vena cava syndrome, a large right hilar-suprahilar mass, extensive mediastinal adenopathy, and bilateral supraclavicular metastases. At that point the brachial plexus, esophagus, and larynx move from background anatomy to active planning constraints.
The standard dose in the chemoradiation setting remains 60 Gy in 30 fractions. What matters is how the chapter ties that dose to image quality and setup verification. Shrinking a thoracic PTV without 4D CT and daily guidance is wishful thinking. Keeping a wide PTV after robust motion assessment and daily kV/CBCT is equally hard to defend when the surrounding lung and esophagus are paying the price.
Postoperative NSCLC
In the postoperative setting, the chapter moves away from the large historical fields that once covered the tumor bed, involved nodal levels, bilateral mediastinum, the ipsilateral bronchial stump, and even supraclavicular nodes for superior tumors. With CT-based planning and more complete mediastinal dissections, that approach has largely fallen out of favor.
Many institutions, including the authors’, now use a limited mediastinal approach that covers the involved nodal regions and the ipsilateral bronchial stump, with consideration of one nodal level above and one below the involved region. The chapter explicitly notes that this mirrors the philosophy used in the Lung ART trial. Since there is no GTV, planning proceeds through CTV, ITV, and then a PTV built with roughly a 0.5 cm ITV-to-PTV expansion, depending on the available IGRT tools.
The postoperative example is concrete. The patient had a 5.8 cm left upper lobe tumor with level 4L disease on EBUS before surgery. After neoadjuvant chemotherapy and resection, margins were negative, but levels 5 and 10L were positive for malignancy. The postoperative field covered the tumor bed, levels 4L, 5, and 7, plus the ipsilateral bronchial stump, and the prescription was 54 Gy delivered as 1.8 Gy x 30 fractions.
This is a more convincing strategy than the older broad-field model because it follows the surgical and pathologic evidence that actually exists. After resection the planning question changes: the issue is no longer where the visible tumor sits, but which postoperative surfaces and nodal chains carry enough residual-risk logic to deserve therapeutic dose.
SCLC and consolidative thoracic radiotherapy
In SCLC, the recommended target definition changes less than many teams expect. The chapter states that there is no single standard GTV-to-CTV margin, but 0.5 to 1.0 cm is acceptable and often includes the ipsilateral hilum. The CTV-to-PTV margin then follows the same logic used in NSCLC, with smaller margins only when motion management and daily image guidance justify them.
The case shown is limited-stage cT2N2 SCLC with right paratracheal and right hilar masses, involvement of the anterior mediastinum, and contiguous extension into the right hilum and precarinal nodes. The authors used an involved nodal approach covering the appropriate mediastinal and hilar regions. The prescribed regimen was 45 Gy as 1.5 Gy x 30 fractions BID, with 0.6 cm expansion from iGTV to iCTV and another 0.5 cm from iCTV to PTV.
For limited-stage disease, the standard dose options remain 45 Gy in BID 1.5 Gy fractions with chemotherapy or 66 to 70 Gy in daily 2.0 Gy fractions. For extensive-stage disease treated in a consolidative or palliative thoracic setting, the chapter gives a standard range of 30 to 45 Gy in ten fractions. The field philosophy remains involved in both settings; what changes is the intent and the fractionation.
Accepted dose regimens
Table 13.1 is useful because it translates the contouring discussion into prescription decisions. The staging language cited in the chapter follows the eighth edition of the AJCC, and the text also notes that normal tissue constraints depend on total dose and fraction count, with guidance from QUANTEC-type analyses.
Accepted radiotherapy regimens for lung cancer
The table below reproduces the regimens listed by the authors for NSCLC and SCLC. It works best as a quick planning cross-check between clinical scenario, tumor location, and treatment intent.
| Clinical scenario | Accepted doses |
|---|---|
| NSCLC, stage I, peripheral SBRT | Variable: includes 54 Gy in 18 Gy fractions, 48 Gy in 12 Gy fractions, 50 Gy in four fractions, and 50 Gy in five fractions |
| NSCLC, stage I, central SBRT | Variable: includes 50 Gy in five fractions, 70 Gy in ten fractions, and 60 Gy in eight fractions |
| NSCLC, stage II-III, standard fractionation | 60 Gy in daily 2 Gy fractions |
| Postoperative | 50-54 Gy in 1.8-2.0 Gy fractions for R0 resection 54-60 Gy in 1.8-2.0 Gy fractions for R1 resection 60 Gy in 2.0 Gy fractions, with consideration of concurrent chemotherapy, for R2 resection |
| SCLC, limited stage | 45 Gy in 1.5 Gy BID fractions with chemotherapy OR 66-70 Gy in daily 2.0 Gy fractions |
| SCLC, extensive stage | 30-45 Gy in 3.0 Gy fractions for consolidative chest radiation |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 13.1)
When CBCT changes the plan
CBCT is not only a setup verification tool. In thoracic disease it can reveal that the original plan no longer matches the current anatomy. The chapter closes with a metastatic pulmonary lesion treated with 45 Gy in 15 fractions. As treatment progressed, lung aeration improved and CBCT showed that adaptive replanning was needed.
That short example captures the chapter’s larger message. Respiratory motion, day-to-day setup, and thoracic anatomy are dynamic variables. If the lung re-expands, the lesion shifts, or the relationship to the esophagus changes, holding onto the first plan can become less accurate than acknowledging early that the anatomy has moved on.
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