Soft Tissue Sarcoma - Board Review Summary

PART I - FOUNDATIONAL RATIONALE FOR RT IN EXTREMITY STS

Limb-Sparing Surgery +/- RT: Two Foundational RCTs

Trial	Design	Local recurrence / control	Key finding
NCI External Beam Yang JCO 1998	Locally resectable extremity STS, GTR without violating tumor; postop randomization. Wide field 45 Gy then cone-down to clips 63 Gy.	High-grade: 0% RT vs 22% no RT. Low-grade: 4% RT vs 37% no RT.	Local-control benefit in both grades. No OS or distant-metastasis difference.
MSKCC Brachytherapy Harrison IJROBP 1993	Extremity and superficial trunk STS, GTR; intra-op randomization. 45 Gy in 4-6 days, single-plane Ir-192, scar/drain holes not treated, skin ≤20 Gy.	Surgery + brachy local control 82% vs surgery 69% overall. High-grade: 11% vs 34% recurrence. Low-grade: no significant benefit.	Brachy benefit was limited to high-grade disease. Wound breakdown was the main complication.

Key distinction: NCI EBRT showed LC benefit regardless of grade; MSKCC brachy, which did not treat the scar or drain holes, showed benefit mainly in high-grade disease. This supports scar coverage in EBRT target design and suggests low-grade STS should not rely on brachytherapy alone.

Indications for RT

The ASTRO adult STS guideline recommends RT for localized extremity or truncal STS when oncologic resection is planned and the patient is at increased risk for local recurrence.
Expert pathology and radiology review plus multidisciplinary evaluation are recommended before treatment.
Factors associated with local recurrence include positive margins, tumor grade, histology, tumor size, site, and morbidity of salvage resection.

Practical takeaway: conventionally fractionated, highly conformal pre-op RT followed by surgery remains the preferred backbone for localized extremity / trunk-wall STS when RT is indicated. Hypofractionation and immunotherapy are important frontiers, but they should not erase the default 50 Gy / 25 fx paradigm.

Management Paradigm + Dose Anchors

Clinical situation	Preferred paradigm	Dose / board anchor
Small, superficial, low-grade, widely resectable	Surgery alone can be appropriate after expert review.	RT omission is most defensible when salvage morbidity is low and margins are clean.
Deep, large, high-grade, close critical structures, or morbid salvage	Limb-sparing surgery + RT.	Pre-op RT preferred: 50 Gy / 25 fx.
Surgery already done first / adverse pathology found	Post-op RT if re-resection is not enough or not feasible.	45-50.4 Gy then cone-down to total 60-63 Gy if R0, 66-68 Gy if R1.
Unplanned excision / "whoops" surgery	Restage, expert pathology review, MRI of operative bed, then planned re-excision +/- RT.	Treat based on residual-disease risk and final oncologic plan, not the accidental operation alone.
Positive margin after pre-op RT	Re-resection if feasible; do not reflexively add a post-op EBRT boost.	Routine boost is especially hard to justify when the R1 margin is planned at bone or neurovascular structures.
Adult elective nodes	No routine elective nodal irradiation.	Exception: alveolar rhabdomyosarcoma; evaluate nodes for nodal-prone histologies.
High-risk UPS / pleomorphic or dedifferentiated LPS of extremity	Consider perioperative pembrolizumab with pre-op RT in a SARC032-like patient.	Do not generalize to all STS histologies.

Workup / Histology-Specific Imaging Pearls

Scenario	Board-style move	Why it matters
Extremity / trunk mass	MRI with contrast before biopsy; core needle biopsy planned in the future resection field.	Bad biopsy tracts create avoidable target-volume and surgical problems.
Staging most extremity STS	CT chest.	Lung is the dominant metastatic site.
Retroperitoneal / visceral sarcoma	CT chest / abdomen / pelvis with expert sarcoma surgery review.	Resectability and organ-at-risk geometry drive local therapy.
Myxoid liposarcoma	Consider spine / whole-body imaging.	Unusual extrapulmonary and osseous / paraspinal metastatic pattern.
Alveolar soft part sarcoma or angiosarcoma	Consider brain imaging in appropriate scenarios.	These histologies have higher CNS-metastasis concern than typical STS.
Nodal-prone STS	Evaluate regional nodes for clear cell sarcoma, epithelioid sarcoma, angiosarcoma, and rhabdomyosarcoma.	Most adult STS does not need elective nodal RT, but these are the exam exceptions.

PART II - PRE-OP vs POST-OP RT

NCIC SR2

NCIC SR2 / O'Sullivan randomized extremity STS to pre-op 50 Gy vs post-op 66 Gy. Equivalent LC, DFS, and OS. Acute wound complications: 35% pre-op vs 17% post-op. Late toxicity favored pre-op RT: fibrosis, edema, and joint stiffness were worse after post-op RT because of the higher dose and larger volume.

ASTRO 2021 KQ2: Pre-operative RT is recommended over post-op RT when both are appropriate. The reason is the burden of permanent late toxicity, not better tumor control. Post-op RT still has a role when surgery occurred first, unexpected adverse pathology is found, or wound-healing risk outweighs late functional concerns.

Trade-offs Summary Table

	Pre-op RT	Post-op RT
Dose	50 Gy	60-66 Gy
Volume	Smaller; based on gross tumor + margins.	Larger; based on operative bed + margins.
Acute toxicity	More wound complications; usually reversible.	Fewer wound complications.
Late toxicity	Less fibrosis, edema, stiffness, fracture risk.	More fibrosis, edema, stiffness, and fracture risk.

PART III - TARGET VOLUMES AND DOSE

Pre-op RT Target Volumes

GTV: T1 post-contrast MRI fused to planning CT.
CTV: GTV + 4 cm longitudinal + 1.5 cm radial, edited at intact fascia and bone. Peritumoral edema visible on T2 MRI should be manually incorporated, since satellite tumor cells may extend several centimeters beyond the visible mass.
PTV: CTV + 5-10 mm per institutional practice and IGRT.

Post-op RT Target Volumes

CTV1 to 45-50.4 Gy: operative bed + 1.5 cm radial + 4 cm longitudinal. If the longitudinal expansion is shorter than the scar, extend to cover the scar.
CTV2 cone-down to about 60 Gy: GTV/tumor bed + 1-1.5 cm radial + 2 cm longitudinal.
Positive-margin region: boost around clips or known positive-margin zone to reach at least 64 Gy.

ASTRO Dose Recommendations

Setting	Dose / fractionation	Notes
Pre-op RT	50 Gy / 25 fx	Standard recommendation.
Post-op first course	45-50.4 Gy / 25-28 fx	Initial large-volume course.
Post-op cone-down	+10-16 Gy to total 60-63 Gy	Negative margins.
Microscopic positive margin	Total 66-68 Gy	DeLaney-style principle: LC improves when total dose exceeds about 64 Gy.

OAR Constraints

OAR	Conventional 25 x 2 Gy constraint	Associated toxicity risk
Skin / limb circumference	Spare at least 2 cm strip of circumference; V20 <100% circumference.	Chronic ulceration, infection, lymphedema.
Bone (weight-bearing)	V40 <64%; mean <37 Gy; max <59 Gy to 2 cc.	Fracture.
Femoral / humeral head	V50 <5%; V45 <25-50%.	Fracture, avascular necrosis.
Joint	V50 ≤50%.	Contracture, pain, edema, decreased ROM.
Large-field factors	Field length >35 cm; large circumferential coverage.	Edema, chronic ulceration.

Wound complication mitigation in pre-op RT: avoid bolus and contract the target slightly off the skin where appropriate. Elective nodal irradiation is not recommended for most adult STS. The classic exception is alveolar rhabdomyosarcoma; nodal evaluation should also be kept in mind for clear cell sarcoma, epithelioid sarcoma, angiosarcoma, and rhabdomyosarcoma.

PART IV - HYPOFRACTIONATION DEBATE

Practical Hypofractionation Position

Regimen	How to frame it	Oral-board takeaway
50 Gy / 25 fx	Current standard pre-op backbone.	Use this as the comparator, especially with modern IG-IMRT.
42.75 Gy / 15 fx	Most balanced moderate-hypofractionated approach.	Promising, convenient, and closest to standard by EQD2; still not a universal replacement.
30 Gy / 5 fx	Convenient 1-week approach.	Reasonable only in selected cases / protocols; counsel delayed wound healing and fracture uncertainty.
25 Gy / 5 fx	Short course but likely underdosed for STS tumor control.	Not the preferred dose-equivalent 5-fraction regimen.
35-40 Gy / 5 fx	Aggressive 5-fraction treatment.	Avoid as routine pre-op extremity STS therapy because late toxicity / amputation concerns dominate.

How to say it cleanly: hypofractionated pre-op RT is attractive and increasingly studied, but the safest board answer is that standard pre-op 50 Gy / 25 remains the benchmark. If using hypofractionation, explain the biologic dose, wound-healing plan, bone constraints, and long-term toxicity uncertainty.

Linear-Quadratic Framework (alpha/beta = 4 for tumor, 2 for late toxicity)

Regimen	EQD2 tumor	EQD2 late toxicity	Delta vs 50/25
25 x 2 Gy (50 Gy)	50 Gy	50 Gy	Reference.
5 x 5 Gy	37.5 Gy	44 Gy	Underdosed for tumor.
5 x 6 Gy	50 Gy	60 Gy	Higher late-toxicity burden.
5 x 7 Gy	64 Gy	79 Gy	Substantially higher late-toxicity burden.
5 x 8 Gy	80 Gy	100 Gy	Very high late-toxicity burden.
15 x 2.85 Gy	49 Gy	52 Gy	Closest moderate hypofractionated analog to standard.

Key Hypofractionation Trials

Trial	N / follow-up	Dose	Local control	MWC	Key caveat
Standard Benchmark (RTOG 0630)	79 / 43 mo	25 x 2 Gy	2y 94%	37%	IG-IMRT reduced late fibrosis/stiffness to <5%.
Kosela-Paterczyk	311 / 57 mo	5 x 5 Gy	5y LRFS 81%	24-32%	Likely underdosed.
Kalbasi	52 then 110 / 29 then 37 mo	5 x 6 Gy	2y 91.7%, 5y 85.7%	30-32%	Delayed wound healing and lower-extremity signal.
Leite	25 / 21 mo	5 x 8 Gy	100% crude LRFS	28%	Amputation/complication signal makes this unattractive.
Bedi	32 / 36 mo	5 x 7 Gy	100% crude	25%	Fibrosis and fracture concerns.
HYPORT-STS	120 / 24 to 43 mo	15 x 2.85 Gy	4y LRFS 93%	31%	Low fibrosis/edema/stiffness; bone fracture still present.

The "SR2 Triad" of Late Toxicity - Head-to-Head

Regimen	Fibrosis (G2+)	Edema (G2+)	Joint stiffness (G2+)
NCIC-SR2 (25 x 2 Gy)	32%	15%	18%
RTOG 0630 (25 x 2 Gy IG-IMRT)	5%	5%	4%
Kosela 5 x 5 Gy	<1% severe	3%	NR
Kalbasi 5 x 6 Gy	11%	4%	11%
Bedi 5 x 7 Gy	35% G2+; 9% G3	NR	NR
HYPORT-STS 15 x 2.85	3%	3%	No G2+

RTOG 0630 is the modern benchmark for conventionally fractionated pre-op IG-IMRT. It reduced fibrosis, edema, and joint stiffness dramatically without compromising control. Hypofractionated regimens should be compared against this modern standard, not just against NCIC-SR2.

Three Underappreciated Hypofractionation Toxicities

(1) Amputations: especially prominent in the most aggressive regimens, including Leite 5 x 8 Gy.
(2) Delayed wound healing: Kalbasi reported a clinically important subset of wounds still unclosed beyond 180 days.
(3) Bone fracture / ORN: uncommon but clinically important and often delayed, including fractures seen after HYPORT-STS and 5 x 6 Gy experience.

Ongoing Hypofractionation Trials

Mayo Clinic: phase II, 15 x 2.85 Gy pre-op.
NKI: randomized phase II, 25 x 2 Gy vs 14 x 3 Gy.
UCLA / Stanford: ongoing phase II of 5 x 6 Gy.

PART V - RECENT PRACTICE-CHANGING RANDOMIZED TRIALS

SU2C-SARC-032 - Pembrolizumab + RT for Extremity UPS / LPS

SU2C-SARC-032 randomized patients with stage III extremity STS with UPS or pleomorphic / dedifferentiated liposarcoma >5 cm. Pre-op 50 Gy / 25 fx vs the same RT plus perioperative pembrolizumab. 2y DFS 67% vs 52%. G3-4 toxicity 56% vs 31%. Major wound complications were not significantly different.

Why this matters: this is the first positive randomized trial integrating immunotherapy into the pre-op RT paradigm for extremity pleomorphic STS. But the eligible subset was narrow, and toxicity was substantially higher, so this should not be generalized to all STS histologies.

STRASS - Retroperitoneal Sarcoma

STRASS randomized patients with primary resectable retroperitoneal STS to pre-op 50.4 Gy IMRT + surgery vs surgery alone. No difference in abdominal recurrence-free survival overall. Peri-operative complications were high but similar between groups.

STRASS - Post-hoc and STREXIT Pooled Analysis

Liposarcoma subgroup in STRASS: post-hoc signal suggesting benefit from pre-op RT, especially for WDLPS and lower-grade DDLPS.
STRASS + STREXIT pooled analysis: strengthened that signal, with HR 0.61 for ARFS in liposarcoma.

Current interpretation: retroperitoneal RT remains a case-by-case multidisciplinary decision. Pre-op RT is often favored for selected liposarcomas, especially WDLPS. Post-op RT for retroperitoneal STS is not recommended.

Retroperitoneal Sarcoma Paradigm + Dose Anchors

RPS situation	Preferred paradigm	Board anchor
Primary resectable RPS overall	Expert en bloc surgery is the core curative treatment.	Routine RT for every RPS patient is not supported by STRASS.
WDLPS / lower-grade DDLPS, expected close posterior or medial margin	Consider pre-op RT in multidisciplinary discussion.	50-50.4 Gy pre-op IMRT is the usual anchor.
High-grade leiomyosarcoma or high distant-risk biology	Systemic therapy / trial discussion often matters more than RT.	Local RT is less compelling when distant relapse is dominant.
Post-op RPS after resection	Avoid routine post-op RT.	Large bowel / kidney / liver often fall into the operative bed; toxicity and target uncertainty are major problems.

PART VI - SPECIAL HISTOLOGIES AND BONE-SARCOMA QUICK HITS

Histology-Specific Board Pearls

Entity	Local / systemic pattern	RT anchor
Myxoid liposarcoma	Very radiosensitive; can shrink dramatically during pre-op RT; unusual extrapulmonary / osseous spread.	Standard 50 Gy / 25; selected dose-reduction data support 36 Gy / 18, but this is not a blanket standard.
Desmoid tumor	Locally aggressive, non-metastasizing; spontaneous stabilization/regression is common.	Active surveillance first when safe; RT about 50-56 Gy for progressive symptomatic disease when surgery is morbid or not feasible.
Angiosarcoma	High local and distant risk; scalp/face disease often has field-cancerization behavior.	Wide-field adjuvant or definitive RT often needed; nodal and brain-risk thinking depends on site and presentation.
Rhabdomyosarcoma / Ewing family tumor	Systemic therapy is mandatory; local therapy is surgery, RT, or both depending on response and function.	Ewing definitive RT commonly 55.8 Gy; microscopic residual about 50.4 Gy.
Chordoma / skull-base chondrosarcoma	Bone tumors, not classic STS, but common sarcoma-board material; local control dominates.	Maximal safe resection plus high-dose particle therapy when feasible, often roughly 70-78+ Gy(RBE).

Do not flatten sarcoma into one disease: pleomorphic UPS, myxoid liposarcoma, retroperitoneal liposarcoma, angiosarcoma, desmoid, Ewing, and chordoma behave very differently. On boards, histology often changes staging workup, systemic therapy urgency, nodal thinking, and dose confidence.

PART VII - CROSS-CUTTING HIGH-YIELD POINTS

Image before biopsy: extremity / trunk STS workup starts with MRI and planned core biopsy so the tract can be resected.
Staging is histology-aware: CT chest is the usual anchor, but myxoid LPS, ASPS, angiosarcoma, RMS, and Ewing-like tumors may need additional site-specific imaging.
NCI EBRT: improves local control in both low- and high-grade extremity STS, without improving OS.
MSKCC brachy: benefit was limited to high-grade disease, and scar/drain-hole omission matters.
NCIC SR2: pre-op and post-op RT give equivalent LC/DFS/OS; pre-op causes more wound problems but less permanent late toxicity.
Extremity/trunk-wall guidance: conventionally fractionated pre-op RT remains the preferred standard when RT is indicated.
ASTRO 2021 dose standards: pre-op 50 Gy / 25 fx; post-op 45-50.4 Gy plus boost to 60-66+ Gy depending on margin status.
Pre-op CTV: GTV + 4 cm longitudinal + 1.5 cm radial, edited anatomically and including relevant edema.
Post-op CTV1: operative bed + 1.5 cm radial + 4 cm longitudinal; include the scar when needed.
Elective nodal RT is generally not indicated in adult STS, except alveolar RMS; evaluate nodes for clear cell, epithelioid, angiosarcoma, and RMS.
Bone constraints matter, especially in weight-bearing bones, because fracture is rare but serious.
RTOG 0630 is the modern conformal/IG-IMRT benchmark for low late toxicity.
Moderate hypofractionation such as 15 x 2.85 Gy appears more balanced than more aggressive 5-fraction schedules.
Three hypofractionation complications to remember: amputations, delayed wound healing, and delayed fracture/ORN.
Myxoid liposarcoma: radiosensitive; standard 50/25 works well, and 36/18 dose reduction is a selected-data pearl.
SU2C-SARC-032: positive DFS signal for pembrolizumab + pre-op RT in high-risk extremity UPS / pleomorphic or dedifferentiated LPS, but with substantially more G3-4 toxicity.
STRASS: negative overall for retroperitoneal STS, with a possible selective benefit in liposarcoma.
Retroperitoneal post-op RT: generally a hard no.
Desmoid: active surveillance first when safe; RT is for selected progressive symptomatic disease when other local options are unattractive.

CONSOLIDATED DOSE TABLE

Setting	Dose / regimen	Comment
Standard pre-op extremity / trunk STS	50 Gy / 25 fx	Preferred backbone when RT is indicated.
Post-op first course	45-50.4 Gy / 25-28 fx	Large-volume operative-bed phase.
Post-op negative-margin total	60-63 Gy	Typical total after cone-down.
Post-op microscopic positive margin	66-68 Gy	Positive-margin region boosted around clips / high-risk bed.
Post-op brachytherapy	45 Gy in 4-6 days	Classic MSKCC LDR Ir-192 approach; scar/drain omission caveat.
HYPORT-STS	42.75 Gy / 15 fx	Moderate hypofractionated pre-op regimen.
5-fraction dose-equivalent hypofractionation	30 Gy / 5 fx	Promising but not universal; wound/fracture uncertainty remains.
Avoid-routine aggressive hypofractionation	35-40 Gy / 5 fx	Late toxicity and amputation concerns.
Myxoid liposarcoma dose reduction	36 Gy / 18 fx	Selected radiosensitive-histology strategy.
Retroperitoneal sarcoma pre-op RT	50-50.4 Gy	Selective, especially WDLPS / lower-grade DDLPS.
Desmoid tumor RT	50-56 Gy	For selected progressive symptomatic disease.
Ewing definitive RT	55.8 Gy	With systemic therapy; postoperative dose depends on residual disease.
Ewing microscopic residual	50.4 Gy	Common post-op anchor.
Chordoma / skull-base chondrosarcoma	70-78+ Gy(RBE)	Particle therapy often favored when feasible.

KEY LANDMARK TRIALS (memorize)

Trial	Disease	One-line takeaway
NCI EBRT	Extremity STS, post-op	RT improved LC in both high- and low-grade disease; no OS benefit.
MSKCC Brachy	Extremity/trunk STS	Brachy benefit was confined to high-grade disease.
NCIC SR2	Extremity STS	Pre-op 50 Gy and post-op 66 Gy gave equivalent control; pre-op had more wound issues, less late toxicity.
DeLaney	Positive-margin STS	LC improved when total dose exceeded 64 Gy.
White	STS microscopic extent	Satellite tumor can extend several centimeters beyond the main mass.
Haas / RTOG contouring era	STS contouring	Foundational target-volume guidance for pre-op and post-op RT.
RTOG 0630	Extremity STS IG-IMRT	Modern IMRT markedly reduced the classic late-toxicity triad.
HYPORT-STS	Extremity STS	15 x 2.85 Gy produced strong LRFS with relatively favorable functional toxicity.
Kalbasi	Extremity STS	5 x 6 Gy showed promising control but notable wound-healing concerns.
Kosela-Paterczyk	Extremity STS	5 x 5 Gy likely underdosed compared with standard pre-op therapy.
Leite	Extremity STS	5 x 8 Gy achieved control but at unacceptable complication cost.
SU2C-SARC-032	High-risk extremity UPS / pleomorphic or dedifferentiated LPS	Pembrolizumab + pre-op RT improved 2y DFS, with higher toxicity.
STRASS	Retroperitoneal sarcoma	Pre-op RT did not improve ARFS overall.
STRASS + STREXIT pooled	Retroperitoneal liposarcoma	Suggested a liposarcoma-specific ARFS benefit from pre-op RT.
DOREMY / myxoid LPS dose-reduction experience	Myxoid liposarcoma	36 Gy / 18 is a selected radiosensitive-histology de-escalation pearl.
Desmoid consensus era	Desmoid tumor	Active surveillance is the default first move when safe.