Soft Tissue Sarcoma — Board Review Summary

PART I — FOUNDATIONAL RATIONALE FOR RT IN EXTREMITY STS

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

TrialDesignLocal Recurrence (5y)Key Finding
NCI External Beam
(Yang JCO 1998)		Locally resectable extremity STS, GTR without violating tumor; post-op randomization. 71 no RT / 78 RT. Wide field 45 Gy then cone-down to clips 63 Gy (1.8/fx)High-grade: 0% RT vs 22% (p=0.003)
Low-grade: 4% vs 37% (p=0.016)		Median follow-up 9.6y. LC benefit in both grades. No OS or DM difference.
MSKCC Brachytherapy
(Harrison IJROBP 1993)		Extremity and superficial trunk STS, GTR; intra-op randomization. 86 no brachy / 78 brachy. 45 Gy in 4-6 days, single-plane Ir-192, scar/drain holes not treated, skin ≤20 GyS+B 82% vs S 69% (p=0.04) overall
High-grade: 11% vs 34% (p=0.0025)
Low-grade: 33% vs 24% (NS)		Median follow-up 76 mo. Brachy benefit 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 only 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 (ASTRO 2021 KQ1 — Salerno PRO 2021)

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

PART II — PRE-OP vs POST-OP RT

NCIC SR2 (O'Sullivan Lancet 2002; long-term JCO 2004)

Extremity STS randomized 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 RTPost-op RT
Dose50 Gy60-66 Gy
VolumeSmaller; based on gross tumor + marginsLarger; based on operative bed + margins
Acute toxicityMore wound complications; usually reversibleFewer wound complications
Late toxicityLess fibrosis, edema, stiffness, fracture riskMore fibrosis, edema, stiffness, and fracture risk

PART III — TARGET VOLUMES AND DOSE (ASTRO 2021 KQ3)

Pre-op RT Target Volumes (Haas IJROBP 2012)

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 2021 Dose Recommendations (Salerno PRO 2021)

SettingDose / FractionationNotes
Pre-op RT50 Gy / 25 fxStandard recommendation
Post-op first course45-50.4 Gy / 25-28 fxInitial large-volume course
Post-op cone-down+10-16 Gy to total 60-63 GyNegative margins
Microscopic positive marginTotal 66-68 GyDeLaney: improved LC above 64 Gy

OAR Constraints (Stinson, Wang, Dickie)

OARConventional 25 x 2 Gy constraintAssociated toxicity risk
Skin / limb circumferenceSpare at least 2 cm strip of circumference; V20 <100% circumferenceChronic ulceration, infection, lymphedema
Bone (weight-bearing)V40 <64%; mean <37 Gy; max <59 Gy to 2 ccFracture
Femoral / humeral headV50 <5%; V45 <25-50%Fracture, avascular necrosis
JointV50 ≤50%Contracture, pain, edema, decreased ROM
Large-field factorsField length >35 cm; large circumferential coverageEdema, 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 adult STS, with the notable exception of alveolar rhabdomyosarcoma.

PART IV — HYPOFRACTIONATION DEBATE (Current Controversy)

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

RegimenEQD2 tumorEQD2 late toxicityDelta vs 50/25
25 x 2 Gy (50 Gy)50 Gy50 GyReference
5 x 5 Gy37.5 Gy44 GyUnderdosed for tumor
5 x 6 Gy50 Gy60 GyHigher late-toxicity burden
5 x 7 Gy64 Gy79 GySubstantially higher late-toxicity burden
5 x 8 Gy80 Gy100 GyVery high late-toxicity burden
15 x 2.85 Gy49 Gy52 GyClosest moderate hypofx analog to standard

Key Hypofractionation Trials

TrialN / Follow-upDoseLocal ControlMWCKey Caveat
Kosela-Paterczyk311 / 57 mo5 x 5 Gy5y LRFS 81%24-32%Likely underdosed
Kalbasi52 then 110 / 29 then 37 mo5 x 6 Gy2y 91.7%, 5y 85.7%30-32%Delayed wound healing and lower-extremity signal
Leite25 / 21 mo5 x 8 Gy100% crude LRFS28%16% amputations, all for complications
Bedi32 / 36 mo5 x 7 Gy100% crude25%Fibrosis and fracture concerns
HYPORT-STS120 / 24 to 43 mo15 x 2.85 Gy4y LRFS 93%31%Low fibrosis/edema/stiffness; bone fracture still present

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

RegimenFibrosis (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% severe3%NR
Kalbasi 5 x 6 Gy11%4%11%
Bedi 5 x 7 Gy35% G2+; 9% G3NRNR
HYPORT-STS 15 x 2.853%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 14-16% 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 (Mowery Lancet 2024) — Pembrolizumab + RT for Extremity UPS

Randomized trial in stage III extremity STS with UPS/pleomorphic histologies >5 cm. 143 randomized, 126 evaluable. Pre-op 50 Gy / 25 fx vs the same RT plus concurrent and adjuvant pembrolizumab. 2y DFS 67% vs 52% (HR 0.61). 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 (Bonvalot Lancet Oncol 2020) — Retroperitoneal Sarcoma

Randomized trial in primary resectable retroperitoneal STS. Pre-op 50.4 Gy IMRT + surgery vs surgery alone. No difference in abdominal recurrence-free survival overall (HR 1.01). 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.

PART VI — CROSS-CUTTING HIGH-YIELD POINTS

  • 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.
  • 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.
  • 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-fx schedules.
  • Three hypofx complications to remember: amputations, delayed wound healing, and delayed fracture/ORN.
  • SU2C-SARC-032: positive DFS signal for pembrolizumab + pre-op RT in high-risk pleomorphic extremity STS, 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.

KEY LANDMARK TRIALS (memorize)

TrialDiseaseOne-line takeaway
NCI EBRT (Yang JCO 1998)Extremity STS, post-opRT improved LC in both high- and low-grade disease; no OS benefit
MSKCC Brachy (Harrison 1993)Extremity/trunk STSBrachy benefit was confined to high-grade disease
NCIC SR2 (O'Sullivan 2002)Extremity STSPre-op 50 Gy and post-op 66 Gy gave equivalent control; pre-op had more wound issues, less late toxicity
DeLaneyPositive-margin STSLC improved when total dose exceeded 64 Gy
WhiteSTS microscopic extentSatellite tumor can extend several centimeters beyond the main mass
HaasSTS contouringFoundational target-volume guidance for pre-op and post-op RT
RTOG 0630Extremity STS IG-IMRTModern IMRT markedly reduced the classic late-toxicity triad
HYPORT-STSExtremity STS15 x 2.85 Gy produced strong LRFS with relatively favorable functional toxicity
KalbasiExtremity STS5 x 6 Gy showed promising control but notable wound-healing concerns
Kosela-PaterczykExtremity STS5 x 5 Gy likely underdosed compared with standard pre-op therapy
LeiteExtremity STS5 x 8 Gy achieved control but at unacceptable complication cost
SU2C-SARC-032 (2024)High-risk extremity UPS/pleomorphic STSPembrolizumab + pre-op RT improved 2y DFS, with higher toxicity
STRASS (2020)Retroperitoneal sarcomaPre-op RT did not improve ARFS overall
STRASS + STREXIT pooledRetroperitoneal liposarcomaSuggested a liposarcoma-specific ARFS benefit from pre-op RT