To evaluate the disease control, survival results, and tolerance of intraoperative electron beam radiotherapy (IOERT) as a component of treatment for retroperitoneal soft tissue sarcomas.

Between March 1981 and September 1995, 87 patients with primary (n = 43) or recurrent (n = 44) retroperitoneal or intrapelvic sarcomas received IOERT as a component of treatment at the Mayo Clinic. The tumors were high grade in 54 patients (62%) and low grade in 33 (38%). The median tumor size was 10 cm (range 2-36). All patients underwent maximal surgical resection with IOERT; in 72 patients, only microscopic or no residual tumor remained. The IOERT doses ranged from 8.75 to 30 Gy (median 15). All primary tumors received external beam irradiation (EBRT) with a median dose of 48.6 Gy. Thirty-four of the 44 recurrent tumors received EBRT to a median dose of 45 Gy. All patients were followed prospectively for outcome and toxicity evaluation.

The median follow-up, based on 46 patients (53%) currently alive, was 3.5 years. The overall estimated 5-year survival was 47%. For patients with tumors > or = 10 cm, the 5-year overall survival was significantly poorer (28%) than for those with smaller lesions (60%) (p = 0.01). Neither primary vs. recurrent status nor tumor grade had a significant impact on survival. Patients with gross residual tumor had a marginally significantly poorer survival compared with patients with microscopic or no residual tumor, with a 5-year survival rate of 37% and 52%, respectively (p = 0.08). A total of 49 patients (56%) experienced failure, including 20 local recurrences (23%). The median time to failure was 2.3 years. Four recurrences were within the IOERT field, 3 within the IOERT and EBRT field, and 13 within the EBRT field alone. The 3- and 5-year estimated local control rate was 77% and 59%, respectively. Local control was marginally significantly affected by the amount of residual tumor, with a 5-year local control rate of 41% for those with gross residual tumor, 60% for those with microscopic residual tumor, and 100% for those with no residual tumor (p = 0.09). Gastrointestinal complications were recorded in 12 incidences (Grade 3 or higher toxicity). These complications were believed to be secondary to surgery and/or EBRT in 10 of the 12 cases. Seven patients had fistula formation, and 3 experienced severe proctitis. Grade 3 peripheral neurologic toxicities occurred in 9 patients (10%), but none had pain as a component of their neuropathy.

Retroperitoneal soft tissue sarcomas can be treated with an aggressive combined approach of EBRT, surgery, and IOERT, with acceptable toxicity. Local control in primary disease appears to be improved in this retrospective series with this approach. Distant disease control and options for recurrent disease needs further definition.