EWING SARCOMA - LOCAL TUMOR-CONTROL AND PATTERNS OF FAILURE FOLLOWING LIMITED-VOLUME RADIATION-THERAPY

Sixty children with localized osseous Ewing's sarcoma were treated between 1978 and 1988 with induction chemotherapy (cyclophosphamide, adriamycin), irradiation and/or surgery, and 10 months of maintenance chemotherapy (cyclophosphamide, adriamycin, dactinomycin, vincristine). Following induction chemotherapy, 43 patients received primary radiation therapy to limited radiation volumes defined by post-chemotherapy residual soft tissue tumor extension and initial osseous tumor extent. Irradiation was defined as low dose at 30-36 Gy (median 35 Gy) for 31 cases with objective response to induction chemotherapy and high dose at 50-60 Gy (median 50.4 Gy) for 12 patients with poor response to induction chemotherapy or with tumors greater-than-or-equal-to 8 cm. Overall event-free survival at 5 years is 59% and local tumor control is 68%. Initial failures have been local (12), simultaneous local and distant failures (7), and distant (6). In the surgical resection group, 14 patients had complete resection without radiation therapy, and 3 patients had microscopic residual plus 35-41 Gy; 100% local control has been maintained. In 43 patients with primary radiation therapy group, local tumor control is 58% (p = .004). Despite limited radiation volume, 18/19 local failures occurred centrally within the bone, well within the radiation volume. Imaging response to induction chemotherapy predicted local tumor control in the radiation therapy group: 62% with complete response/partial response versus 17% with no response/progressive disease (p < 0.01). Local tumor control related strongly to primary tumor size in the radiation therapy group; among 31 cases receiving 35 Gy, local tumor control is 90% for lesions < 8 cm versus 52% for tumors greater-than-or-equal-to 8 cm (p = .054). The central pattern of local failure in this experience suggests the effectiveness of limited radiation volume. The overall local tumor control rate following the tested dose level of 35 Gy appears to be inadequate, although results in selected cases with tumors < 8 cm in greatest tumor dimension indicate potential efficacy in a yet limited experience.