Surgery With or Without Radiation Therapy in Treating Patients With Primary Soft Tissue Sarcoma of the Retroperitoneum or Pelvis

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