A phase II trial evaluation selective use of altered radiation dose and fractionation in patients with unresectable rhabdomyosarcoma

Purpose: Between 1987 and 1991, 25 children with advanced rhabdomyosarcoma (20 with IRS Group 3 disease and 5 with Group 4 disease) were entered on a prospective study evaluating selective use of hyperfractionated irradiation (HFI) and reduced-dose conventionally fractionated irradiation (CFI), based on disease status following induction chemotherapy (ifosfamide or melphalan, followed by vincristine, adriamycin, and cyclophosphamide combination) with or without delayed surgery. Methods and Materials: Patients with gross disease following induction chemotherapy with or without delayed surgery, and whose primary tumor sites did not involve the central nervous system, received HFI (n = 12) at 1.1 Gy twice-a-day to 59.4-63.8 Gy total. Patients with parameningeal primaries and intracranial disease extension received HFI with initiation of therapy (n = 2). Those with microscopic disease following induction chemotherapy with or without delayed surgery (n = 11) received reduced-dose CFI to 40 Gy. Active follow-up ranges from 28-75 months (median = 43 months) with no patient lost to follow-up. Results: Eighteen patients (72%) are alive and without disease, including 8 of the children with gross residual disease postinduction therapy. The absolute 2-year continuous local tumor control rate is 86% for all patients. Among the 14 who received HFI, the absolute 2-year continuous local tumor control rate is 75% at 33 to 67 months (median = 38 months) postirradiation. Hyperfractionated irradiation was associated with expected enhancement of acute reactions, which all resolved with conservative medical management. Grade 4 or 5 acute toxicities were not seen. Significant late radiation morbidity has, thus far, been minimal and limited to Grade 1 and 2 events. Among the 11 who received reduced-dose CFI, the absolute 2-year continuous local tumor control rate is 100% at 25 to 70 months (median = 40 months) postirradiation. Conclusion: This limited experience suggests that HFI to a dose level of 60 Gy can be used selectively in children with advanced rhabdomyosarcoma left with gross disease following induction chemotherapy, with or without delayed surgery, with an apparent improvement in local control, and minimization of potential late radiation toxicity. Concurrently, those left with microscopic disease following therapy can be selectively treated with reduced-dose CFI with excellent local control.