Soft tissue sarcoma target delineation starts with compartment anatomy, longitudinal spread, and peritumoral edema. In this chapter excerpt, those elements drive the margins, the choice between preoperative and postoperative radiotherapy, and the way extremity and retroperitoneal disease are planned.
The chapter also stays practical about what changes management most: anatomic location, tumor size, depth relative to the superficial fascia, and pathologic features. For the broader framework behind these planning decisions, see our Target Volume Delineation and Field Setup – Complete Clinical Guide.
In This Article
General planning and delineation principles
The first decision in soft tissue sarcoma is not dose selection. It is anatomic interpretation. The chapter states that STS usually invades longitudinally within muscle and remains confined to its compartment of origin. That pattern is why cranio-caudal margins are often more generous than radial ones, and why bone, the interosseous membrane, and major fascial planes should be exploited during planning, especially in extremity lesions where tissue and function preservation matter.
Peritumoral edema is handled with the same level of seriousness as the visible tumor edge. The text uses the term edema for suspicious peritumoral change and assumes that it may harbor microscopic disease. It also notes that edema is most pronounced in the cranio-caudal direction and ordinarily should be encompassed in the radiotherapy target volume. That point is easy to underestimate on a busy contouring day. In this chapter, it is a central planning rule.
The unplanned excision examples show what happens when this anatomy has already been disturbed. In the posterolateral thigh liposarcoma case from Fig. 32.1, the prior superficial excision breached the fascia of the vastus lateralis without involving the deeper compartment originally. CT simulation used 2.0-mm slices, and the violated fascia becomes the key landmark for reconstructing the area at risk. The lesson is blunt: after surgical error with positive margins, the RT target volume must generously include all disturbed muscle compartments and any other directly involved tissues.
Fig. 32.3 pushes that principle further. The patient had a right pretibial pleomorphic undifferentiated sarcoma measuring 3 cm, staged T1N0M0, closed with a split-thickness graft after unplanned excision, and both radial and deep margins were positive. The recommended sequence was 50 Gy preoperative radiotherapy followed by wide re-excision and free-flap closure. The postoperative GTV was reconstructed from the preoperative CT. The CTV50 extended 3 to 4 cm radially beyond the edge of the skin graft where the positive margins lay, and the deep target included the involved periosteum. A 5 mm bolus plug filled the soft tissue defect anterior to the graft to provide build-up over the deep periosteal margin.
The chapter also inserts a staging note worth remembering. The eighth edition of TNM changed classification, including different size thresholds by anatomic site and removal of depth from staging. That does not make depth irrelevant to planning. It simply means that staging categories and practical target delineation are answering different questions.
Preoperative planning and edema coverage
In the preoperative setting, CT simulation fused with MRI is the backbone of target definition, ideally with the patient already positioned for treatment. That is how the chapter recommends defining both the GTV and the CTV50 on every slice of the planning CT.
The usual preoperative dose is 50 Gy. Gross disease is defined by physical examination and imaging, with T1-weighted contrast-enhanced MRI preferred for the tumor itself. From there, the CTV50 expands 4 cm longitudinally and 1.5 cm radially, limited to but including barriers to spread such as bone or fascia. Suspicious edema, best seen on T2-weighted MRI, is contoured separately and covered with an adequate margin, usually 1 to 2 cm, because it may contain microscopic tumor cells.
Fig. 32.7 shows how far that edema logic can extend. This was a deep grade 2 myxofibrosarcoma, T3N0M0, in the left lateral thigh. The patient received preoperative RT specifically to minimize the necessary treatment volume. CT simulation again used 2.0-mm slice thickness. Extensive edema tracked superiorly and inferiorly and was incorporated into CTV50, with bone limiting the target throughout. The PTV measured 42 cm in length, beyond what the machine could cover with a single-isocenter technique, so planning used dual-isocenter IMRT. The isocenters were placed to approximate the center of both adjoining volumes and co-optimized to maintain uniform PTV coverage.
Fig. 32.8 adds the sagittal correlation between simulation CT and preoperative T2-weighted MRI. The point is not merely illustrative. It shows why preoperative image import and co-registration are necessary to appreciate the full extent of longitudinal edema before the CTV50 is finalized. The chapter pairs that with the usual PTV expansion of 0.5 to 1.0 cm according to institutional practice. In long extremity sarcomas, missing the edema tail is often a more realistic planning risk than missing the central gross tumor.
Even when the tumor appears well contained by fascia, preoperative planning is not minimalist. The contour respects barriers to avoid unnecessary expansion, but it is prepared to include the barrier itself when that is the safer oncologic choice. That is why MRI fusion, treatment-position immobilization, and slice-by-slice contouring are treated here as standard requirements, not optional refinements.
Table 32.1. Suggested target volumes for preoperative extremity STS
This table condenses the preoperative extremity workflow into GTV, CTV50, and PTV50. The structure matters because it ties the visible tumor, the edema, and the anatomic barriers into one contouring strategy instead of treating them as separate problems.
| Target volume | Definition and description |
|---|---|
| GTV | Primary gross disease on physical examination and imaging. T1-weighted contrast-enhanced MRI is preferred. MRI-to-planning-CT co-registration is facilitated when the patient is immobilized in the treatment position. |
| CTV50* | Includes all areas at risk of subclinical spread as defined by the distance from the GTV or edema. Includes the GTV + a 4-cm margin in the longitudinal dimensions and a 1.5-cm margin in the radial dimension, limited to but including any anatomic barrier to tumor spread such as bone or fascia. Suspicious peritumoral edema, best shown on T2-weighted MRI, may contain microscopic tumor cells and should be contoured separately with an adequate margin, usually 1 to 2 cm. For cases of unplanned excision, margins should include the GTVpostop or any residual GTV + all surgically manipulated and disturbed tissues and violated fascia + 4 cm longitudinally and 1.5 cm radially, limited to but including any barrier to tumor spread. |
| PTV50* | CTV50 + 0.5 to 1.0 cm, according to institutional protocol and procedure. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 32.1)
* Suggested gross tumor dose: 2.0 Gy per fraction to 50 Gy.
Postoperative planning and risk-adapted volumes
After an assumed complete resection, postoperative planning has to work without a visible gross tumor. The chapter therefore reconstructs the original tumor site as GTVpostop on the planning CT, using preoperative CT or MRI whenever available. Without that step, the postoperative target risks becoming a map of surgery alone rather than a map of where the tumor actually was.
The usual postoperative dose is 66 Gy, although 60 Gy may be used in low-grade cases with clear margins. For extremity IMRT, the higher-risk CTV66 covers the entire GTVpostop plus the immediate area of surgical change with a 1- to 2-cm longitudinal margin and a 1.5-cm transverse margin. The lower-risk CTV56 expands more broadly, using 4 cm longitudinally and 1.5 cm radially from GTVpostop, while also capturing disturbed tissues, scars, and drain sites if they are not already inside CTV66.
The left thigh pleomorphic rhabdomyosarcoma case in Fig. 32.4 shows how those rules are applied. The tumor was deep, grade 3, staged T3N0M0, and treated postoperatively because margins were negative but close. CT simulation again used 2.0-mm slices. Edema at the superior aspect of GTVpostop was included in CTV56, and the target remained limited by the femoral head and bone throughout. The chapter adds a practical note: when the subcutaneous tissues may have been contaminated, bolus can be applied to the surgical scar for part of the treatment, for example to 50 Gy.
Figs. 32.5 and 32.6 sharpen the postoperative message. The sagittal planning CT is shown alongside preoperative and postoperative MRI to demonstrate that CTV56 is defined by both edema and postoperative change, while the usual PTV margin remains in the 0.5- to 1.0-cm range. The digitally rendered skin image then shows PTV56 including the scar with margin, a reminder that contamination pathways may run along the surgical approach and not only through the deep tumor bed.
Recent postoperative MRI is the preferred tool for identifying suspicious edema and surgically disrupted tissue. By contrast, the decision to include a seroma, lymphocele, or hematoma should not be automatic. The chapter explicitly recommends discussion with the surgeon and review of the operative and pathology reports before deciding whether those collections belong inside the target.
Table 32.2. Suggested target volumes for postoperative extremity STS
The postoperative table separates the highest-risk surgical bed from the broader territory of subclinical risk. That distinction explains why the chapter uses CTV66 and CTV56 together instead of treating the entire postoperative field as one uniform volume.
| Target volume | Definition and description |
|---|---|
| GTVpostop | Should identify the original site of the tumor. Review and import presurgical imaging when contouring on the simulation CT for RT planning to ensure adequate coverage of the original tumor extent. |
| CTV66* | Should encompass the entire GTVpostop + the immediate area of surgical change with a 1- to 2-cm margin in the longitudinal plane and a 1.5-cm margin in the transverse plane. This may, but not always, include all surgically disturbed tissues, scars, and drain sites. |
| PTV66* | CTV66 + 0.5 to 1.0 cm, according to institutional protocol and procedure. |
| CTV56* | Includes all areas at risk of subclinical spread as defined by the distance from the GTVpostop and additional disturbed tissues. Includes the GTVpostop + a 4-cm margin in the longitudinal dimensions and a 1.5-cm margin in the radial dimension, limited to but including any anatomic barrier to disease spread; additional disturbed surgical tissues and any scars or drain sites are ordinarily included with a 1- to 2-cm margin if they are not already in CTV66. Suspicious peritumoral edema should be contoured separately and included with an adequate margin. Like surgically disrupted tissue, it is best identified on a recent postoperative MRI scan. Discussion with the surgeon and review of the surgical and pathology reports help decide whether a seroma, lymphocele, or hematoma should be included. |
| PTV56* | CTV56 + 0.5 to 1.0 cm, according to institutional protocol and procedure. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 32.2)
The table describes a single-phase simultaneous boost technique. The chapter also cites the traditional phased shrinking-field approach: 50 Gy in 25 fractions to all areas of subclinical disease followed by a 16 Gy boost in 8 fractions using a second radiotherapy plan.
* High-risk subclinical dose: 2.0 Gy per fraction to 66 Gy. For lower-risk subclinical regions, 1.69 Gy per fraction to 56 Gy delivered to CTV56.
Residual disease and retroperitoneal STS
When unresectable residual gross disease remains, the chapter escalates to 70 Gy in 2 Gy per fraction, or an equivalent fractionation, as anatomy permits. At that point, organ tolerance becomes a central part of target design rather than a downstream checklist.
Retroperitoneal sarcoma makes that balance obvious. The text describes these tumors as lesions that often grow very large, initially displacing adjacent organs and tissues before eventually invading them. That is one reason preoperative radiotherapy is attractive in this setting. In the right-sided grade 3 undifferentiated pleomorphic retroperitoneal sarcoma from Figs. 32.9 and 32.10, the mass lay against the duodenum, right kidney, and iliac vessels. A small amount of liver was intentionally included in the CTV and PTV on the first three axial slices, multifocal intratumoral calcifications aided daily image guidance for targeted IMRT, and bowel displacement by the tumor was presented as one of the major advantages of preoperative treatment. The chapter also encourages 4D CT simulation here.
For preoperative retroperitoneal IMRT, the suggested gross tumor dose ranges from 50 Gy in 25 fractions to 50.4 Gy in 28 fractions. The CTV uses a 2-cm longitudinal margin and a 0.5- to 2.0-cm radial margin. That radial margin is intentionally adaptable because the contour must include barriers to spread and critical anatomy where appropriate. If the tumor is abutting an intact liver, for example, 0.5 cm of liver is included. Posteriorly, 2-cm margins are usually used to cover fat and vessels.
The renal strategy is equally pragmatic. The ipsilateral kidney may be sacrificed if the contralateral kidney functions acceptably. When that happens, dose to the uninvolved opposite kidney should be kept as low as reasonably achievable. The chapter lists the small bowel, liver, spinal cord, and lungs as additional organs at risk. After those considerations, the PTV adds only 0.5 cm according to institutional protocol.
Table 32.3. Suggested target volumes for retroperitoneal STS
For retroperitoneal disease, the table makes the radial margin intentionally flexible. It ranges from 0.5 to 2.0 cm because the final contour has to balance subclinical spread against critical adjacent anatomy.
| Target volume | Definition and description |
|---|---|
| GTVa | Primary gross disease on physical examination and imaging. |
| CTV | Includes all areas at risk of subclinical spread as defined by the distance from the GTV. Includes the GTV + a 2-cm margin in the longitudinal dimensions and a 0.5- to 2.0-cm margin in the radial dimension, limited to but including any anatomic barrier to tumor spread and critical anatomy. For example, if the tumor is approximating an intact liver, 0.5 cm of liver is included. Posterior 2-cm margins are usually used to include fatty tissues and vessels. The ipsilateral kidney may be sacrificed provided the contralateral kidney has acceptable function. In that setting, dose to the uninvolved opposite kidney should be kept as low as reasonably achievable. Other organs at risk include the small bowel, liver, spinal cord, and lungs. |
| PTV | CTV + 0.5 cm, according to institutional protocol and procedure. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 32.3)
a Suggested gross tumor dose range: 50 Gy in 25 fractions to 50.4 Gy in 28 fractions.
Practical synthesis
Preoperative and postoperative STS planning rely on the same respect for anatomy, but they are not interchangeable workflows. Preoperative planning follows visible tumor and visible edema, uses 50 Gy as the usual dose, and clearly benefits from intact anatomic planes, sometimes enough to reduce the treatment volume substantially. Postoperative planning works backward from a reconstructed tumor site, separates higher-risk and lower-risk subclinical regions through CTV66 and CTV56, and pays far more attention to scars, drains, and surgically disturbed tissue.
The contrast between extremity disease and retroperitoneal disease is just as important. Extremity sarcomas often respect fascial and osseous barriers closely enough for function-preserving planning to use those limits intelligently. Retroperitoneal tumors, by contrast, force the planner into constant negotiation with liver, kidney, bowel, vessels, spinal cord, and lungs. What stays constant across both settings is the discipline: review the original imaging, map the likely route of spread, and never dismiss edema, violated fascia, or contaminated surgical pathways as secondary findings.
For the broader clinical framework that surrounds this sarcoma chapter, return to the main guide in the series. It places these margins and field setup choices inside the larger practice of conformal and intensity-modulated radiotherapy planning.
