Radiocurability of microscopic disease in childhood rhabdomyosarcoma with radiation doses less than 4,000 cGy.

In an attempt to evaluate the radiocurability of microscopic disease in childhood rhabdomyosarcoma (RMS) with total tumor doses of less than 4,000 cGy, we performed a retrospective analysis of all patients with microscopic residual RMS who were treated at the Memorial Sloan-Kettering Cancer Center (MSKCC) during the years 1970 to 1987. There were 32 patients ranging in age from 3 months to 22 years (median, 6 years) with microscopic residual of either (1) a localized primary tumor (MSKCC, stage IB; Intergroup Rhabdomyosarcoma Study [IRS] group IIA), 19 patients; or (2) an involved lymph node region with the primary tumor completely resected (MSKCC stage III; IRS group IIC), 13 patients. Twenty-nine of the 32 patients presented with embryonal histology. All patients were treated with combination chemotherapy (CT) and megavoltage external beam radiotherapy (RT). The RT was delivered in either conventional fractionation of 180 to 200 cGy daily (30 patients) or hyperfractionation of 150 cGy twice daily (two patients). Fifteen patients received RT doses of less than 4,000 cGy with a range of 3,000 to 3,600 cGy and a median value of 3,100 cGy; 17 patients received 4,000 cGy or more with a range of 4,000 to 6,000 cGy and a median value of 4,600 cGy. With a median follow-up of 11 years, the relapse-free survival was 25 of 32 patients (less than 4,000 cGy, 12 of 15; greater than or equal to 4,000 cGy, 13 of 17). The RT local control rate was 30 of 32 (less than 4,000 cGy, 14 of 15; greater than or equal to 4,000 cGy, 16 of 17 [P = .94]). Our results suggest that radiation doses of below 4,000 cGy, when combined with effective multiagent CT, may be sufficient for local control of microscopic disease in childhood embryonal RMS.