SOFT TISSUE SARCOMA-TARGET VOLUME DELINEATION

SIMULATION

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General SIM Principles

Depending on anatomic location. Supine position preferred, prone may be needed. For postoperative cases, wire the scar or the entire field to help with target delineation. Do not specifically target drain sites.

Lower Extremity

Vac-Lock for involved extremity. Distal primaries may need CT scan feet first. Frog leg for proximal thigh cases or when needed to create separation with contralateral extremity or decrease inguinal fold. Can elevate noninvolved leg to facilitate better dosimetry and imaging localized to involved leg.

Upper Extremity

Upper Vac-Lok. Arm position depends on location of primary but is usually akimbo. Consider a prone "swimmers" position or abducted arm.

Distal Extremities

Can consider custom cushion +/− aquaplast mask to help with immobilization

Head and Neck

Prior to SIM, consider dental evaluation/need for stent. Aquaplast mask

Retroperitoneal

Vac-Lock. Generally arms up (depending on tumor position). For lesions above the iliac crests, the scan should be 4D to account for breathing motion.

Dose and Fractionation

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Extremity
  • Preoperative: 50 Gy in 25 fractions (conventional) is the standard fractionation schedule. If hypofractionation is considered, then preferred regimen is 42.75 Gy in 15 fractions (as per HYPORT-STS).
  • Postoperative: 60 Gy at 2 Gy/fx for R0 resection, with field size reduction after 50 Gy.
  • Boost to 64-68 Gy for a positive margin.
  • (Despite a higher boost dose, LR is higher in R1/2 resection; in other words, a higher radiation dose does not make up for lack of R0 resection.)
Considerations

If IMRT preferable for postoperative cases, can also consider a simultaneous-integrated boost technique. (Ex: for R0 resection—CTV2 treated to 59.92 Gy in 28 fractions (2.14 Gy/fx) and CTV1 to 50.4 Gy in 28 fractions (1.8 Gy/fx).

If there are positive margins postoperatively, can do SIB technique in 30 fractions with doses of 66 Gy, 60 Gy, and 54 Gy to the different CTVs.

Retroperitoneal STS - RT Doses

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  • Definitive: 60-66 Gy
  • Preoperative: 50 Gy
  • Postoperative: 60 Gy

Special Clinical Entities

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Adult Extraosseous Ewing Sarcoma
  • Small round blue cell tumor. Very rare. More common in children
  • Translocation t(11;22) or t(21;22) in 95% of cases
  • Upfront intensive chemotherapy for everyone
  • Local tumor treatment is controversial. Consultation at sarcoma specialty center is highly recommended. Often treated with a combined modality approach. However, single modality treatment (either surgery OR can be considered depending on anatomic location and response to chemotherapy
  • RT Doses: Definitive: 60-66 Gy | Preoperative: 50 Gy | Postoperative: 60 Gy
Adult Rhabdomyosarcoma Sarcoma
  • Adults with RMS do worse than pediatric patients
  • Alveolar, embryonal, and pleomorphic subtypes
  • Pediatric RT doses are insufficient. Normally escalate dose closer to standard adult STS doses upward of 60+ Gy in the definitive setting, respecting adjacent normal tissue tolerance
Desmoid Tumors
  • Not technically malignant (does not metastasize) but is a locally aggressive and potentially destructive neoplasm: observed until local progression is painful and/or morbid. The treatment decision is complex and nuanced. Systemic therapies. Radiation therapy is a local control option. We offer it as an upfront treatment option more commonly in older patients when it is a salvage option in younger patients
  • Definitive treatment schema: 56 Gy in 28 fx
Dermatofibrosarcoma Protuberans
  • Uncommon, low-grade sarcoma of the skin with a characteristic t(17;22) translocation
  • Primary treatment is surgery, followed by RT for indeterminant/positive margins or if recurrent disease
  • If they have fibrosarcomatous transformation, local treatment is more in line with STS management with both surgery and RT (preoperative preferred)

IGRT and Planning Directives

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IGRT
  • Related to modality used and body site.
  • Daily kV-aligning to bone typically used. (For 3D planning: consider rotating collimator parallel with long bone for set-up and kV alignment.)
  • Weekly CBCT recommended for adequate coverage as tumors can sometimes change on treatment necessitating an adaptive plan (due to either increased or decreased size of tumor while on treatment).
Planning Directive - Conventional Fractionation
  • Spare at least 1-cm strip of limb circumference/skin
  • Avoid treating entire limb circumference >20 Gy when using IMRT
  • Avoid treating entire femur circumference to ≥50 Gy
  • Spare ½ cross section of weight-bearing bone; V40 < 64%, mean dose ≤ 37 Gy
  • Block part of the joint cavity: V50 <50%
  • Block major tendons: V50 ≤ 50%
Planning Directive - HYPORT Fractionation (15 fractions)
  • Spare 1-cm strip of limb circumference/skin
  • Avoid treating entire limb circumference >17 Gy
  • Avoid treating entire femur circumference to ≥42.75 Gy
  • Spare ½ cross section of weight-bearing bone; V35 < 65%
  • Block part of the joint cavity: V42.75 < 50%
Planning Directive - Retroperitoneal Sarcoma
  • Bowel Bag: Dmax < 54 Gy, V45 < 195 cc
  • Spine: Dmax < 45 Gy
  • Liver: Mean < 25 Gy, V30 < 30%
  • Kidneys: V20 < 30%, mean < 18 Gy
  • Spleen: Mean < 8 Gy
  • Bladder: Dmax < 54 Gy, V30 < 50%
  • Lungs: V20 <10%

Retroperitoneal STS - Target and Technique

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Target (50.4 Gy in 28 fractions)
  • Preoperative: Extremity: GTV + 3-4 cm longitudinally sup/inf along fascial planes and 1.5 cm radially to yield CTV
  • Special case: if subcutaneous tumor: GTV + 3-4 cm circumferential expansion sup/inf and radially, adhering to anatomic barriers
  • Postoperative: Virtual GTV = preoperative GTV (if imaging available) or postoperative bed. CTV1 as above (3-4 cm sup/inf, 1.5 cm radially off of vGTV). Cone down to CTV2 to 60-68 Gy total (vGTV + 2 cm sup/inf, 1.5 cm radially)
  • RPS: GTV + 1.5 cm symmetric margins to yield CTV (allowing 5 mm into bowel). Trim from liver, bone kidney, etc. as per Baldini guidelines
Considerations

CTV expansions can be increased in difficult surgical access areas or superficial spreading histologies. CTVs can be trimmed/carved out of bone if not involved. Do not cover elective nodes for any histology other than alveolar rhabdomyosarcoma. PTV expansions are typically 0.5–1 cm depending on daily imaging techniques

Technique
  • 3DCRT: Consider parallel opposed fields (with nondivergent deep border to spare bone/joint). Other beam arrangements (wedge-pair, obliques, etc.) may be used as well. Asymmetric beam weighting can be used if the tumor is not centrally located.
  • IMRT: Unless 3D planning shows a clear benefit in reduced dose to OAR, IMRT/VMAT is routinely done for improved conformality for proximal lower extremities, thoracic, pelvic, retroperitoneal, head and neck sites.