DISEASE CHARACTERISTICS:

* Histologically confirmed primary soft tissue sarcoma of the retroperitoneum or pelvis (e.g., iliac fossa)

* The following histologies are eligible:

* Alveolar soft part sarcoma
* Anaplastic sarcoma
* Angiosarcoma
* Atypical lipomatous tumor (low-grade liposarcoma)
* Clear cell sarcoma
* Epithelioid sarcoma
* Fibrosarcoma
* Leiomyosarcoma
* Liposarcoma (all subtypes)
* Malignant fibrous histiocytoma
* Malignant peripheral nerve sheath tumor
* Myxofibrosarcoma
* Neurofibrosarcoma
* Spindle cell sarcoma
* Synovial sarcoma
* Unclassified sarcoma
* The following histologies are not eligible:

* Rhabdomyosarcoma
* Extraosseous Ewing's sarcoma
* Primitive neuroectodermal tumor
* Osteosarcoma
* Chondrosarcoma
* Aggressive fibromatosis (desmoid tumor)
* Gastrointestinal stromal tumor
* Sarcomatoid carcinoma
* Hemangiopericytoma
* Retroperitoneal sarcomas located predominantly in the retroperitoneum extending across the inguinal ligament into the abdominal wall are allowed provided that ≥ 90% of the tumor volume is located within the retroperitoneal space

* No bowel obstruction OR history of previous bowel obstruction attributed to retroperitoneal tumor
* Primary non-visceral retroperitoneal masses consistent with sarcoma allowed provided diagnoses of carcinoma, melanoma, and lymphoma are excluded by immunohistochemistry
* Measurable gross disease by abdominopelvic CT scan (with IV and oral contrast) or MRI (with IV contrast)
* Patients must have undergone radiotherapy consultation within the past 30 days to confirm the feasibility of preoperative external-beam radiotherapy
* Patients must have undergone surgical consultation within the past 30 days to confirm and document the feasibility of macroscopically complete resection

* No prior macroscopically incomplete (R2) resection (i.e., partial debulking or subtotal tumor resection with gross residual disease)
* No pelvic sarcoma extending through the sciatic notch
* No clinical or radiographic evidence of probable metastatic disease

* Equivocal pulmonary or liver lesion allowed provided the likelihood of metastatic disease is small
* No sarcoma arising from bone or any retroperitoneal viscus (except the kidney)
* No sarcoma extending across the diaphragm into the thorax
* No recurrent retroperitoneal tumor
* No multifocal disease

PATIENT CHARACTERISTICS:

Age

* 18 and over

Performance status

* ECOG 0-1 OR
* Zubrod 0-1

Life expectancy

* Not specified

Hematopoietic

* WBC ≥ 2,500/mm\^3
* Platelet count ≥ 80,000/mm\^3

Hepatic

* Bilirubin ≤ 1.5 times upper limit of normal (ULN)
* AST ≤ 2.5 times ULN
* Albumin normal\* NOTE: \*Higher levels allowed

Renal

* Creatinine normal
* BUN normal
* Functional kidney confirmed by intravenous pyelogram and/or differential renal isotope scan

Other

* Not pregnant
* Negative pregnancy test
* Fertile patients must use effective contraception during and for 3 months after study participation
* No other malignancy within the past 5 years (except effectively treated basal cell or squamous cell skin cancer) unless patient was curatively treated AND is at low risk for recurrence

PRIOR CONCURRENT THERAPY:

Chemotherapy

* No concurrent chemotherapy for primary tumor

Radiotherapy

* No prior abdominal or pelvic irradiation
* No concurrent intraoperative or postoperative radiotherapy for primary tumor

Surgery

* See Disease Characteristics