Preoperative Spatially Fractionated Radiation Therapy (SFRT) in Soft Tissue Sarcoma (neoSFRT-SARC)

Inclusion Criteria:

* Histologically confirmed soft tissue sarcoma of the extremity or trunk, with tumor size ≥5 cm in greatest dimension (by imaging or clinical examination).
* Disease classified as operable or borderline-resectable as determined by the multidisciplinary tumor board.
* Age ≥18 years at the time of consent.
* Eastern Cooperative Oncology Group (ECOG) performance status 0-2.
* Adequate organ function as defined by:

Absolute neutrophil count ≥1.5 × 10⁹/L; Platelet count ≥100 × 10⁹/L; Hemoglobin ≥9.0 g/dL; Total bilirubin ≤1.5 × upper limit of normal (ULN) (or ≤3 × ULN in patients with Gilbert's syndrome); AST/ALT ≤2.5 × ULN; Creatinine clearance ≥50 mL/min (by Cockcroft-Gault or measured);

* Women of childbearing potential must have a negative serum or urine pregnancy test within 7 days prior to enrollment and agree to use effective contraception during the study treatment period and for at least 3 months after the last study procedure. Men with partners of childbearing potential must agree to use effective contraception during the same period.
* Willing and able to provide written informed consent and comply with all study procedures, including scheduled follow-up visits and blood sample collections.

Exclusion Criteria:

* Prior radiotherapy to the same anatomical site that would result in overlap of radiation fields.
* Distant metastases at the time of enrollment (M1 disease).
* Pregnancy or breastfeeding.
* Active second malignancy requiring systemic therapy within the past 3 years, except for adequately treated basal cell carcinoma, squamous cell carcinoma of the skin, or carcinoma in situ.
* Severe, active comorbidities including but not limited to:

Uncontrolled infection requiring intravenous antibiotics; Decompensated heart failure (New York Heart Association Class III or IV); Myocardial infarction or unstable angina within 6 months; Severe chronic obstructive pulmonary disease or other conditions that would preclude safe radiotherapy or surgery.

* Known hypersensitivity to radiation therapy procedures or inability to undergo required imaging (e.g., MRI contrast allergy not manageable with premedication).
* Concurrent participation in another interventional clinical trial with an investigational agent within 30 days prior to enrollment.
* Any condition that, in the opinion of the investigator, would compromise patient safety, interfere with study compliance, or preclude successful completion of the study procedures.