The challenging role of radiation therapy for very young children with rhabdomyosarcoma

Purpose: To evaluate local control and toxicity for very young children treated with multimodality therapy for rhabdomyosarcoma (RMS). Methods and Materials: From 1990 to 2004, 20 patients ≤36 months at diagnosis were treated at our institution. Nineteen underwent chemotherapy (CMT), surgery and/or intraoperative high-dose-rate brachytherapy (IOHDR), and external-beam radiation (EBRT). Median age was 17 months. Sites included extremity (7), trunk (5), parameningeal (4), orbit (1), head/neck (1), bladder/prostate (1). Histologies consisted of 10 embryonal (53%) and 9 alveolar/undifferentiated (47%). Ten had delayed gross total resection (GTR) at median time of 17 weeks after the start of CMT, and 8 of these underwent IOHDR. Median interval between start of CMT and EBRT was 18 weeks. Median EBRT dose was 36 Gy. EBRT technique was either intensity-modulated (11), three-dimensional (3), or two-dimensional (5). Functional outcome was assessed for patients alive ≥1 year after diagnosis (15) in terms of mild, moderate, or severe deficits. Results: Median follow-up was 33 months for survivors and 23 months for all patients. Two-year actuarial local control, event-free survival, disease-specific survival, and overall survival were 84%, 52%, 74%, and 62%, respectively. All patients who began EBRT ≤18 weeks after the start of CMT had their disease controlled locally. Five have mild deficits and 10 have no deficits. Conclusions: A reduced dose of 36-Gy EBRT after delayed GTR may maximize local control while minimizing long-term sequelae for very young children with RMS, but unresectable tumors (e.g., parameningeal) require higher doses. Normal-tissue-sparing techniques such as intensity-modulated radiation therapy and IOHDR are encouraged. Local control may be maximized when EBRT begins ≤18 weeks after initiation of CMT, but further study is warranted. Longer follow-up is required to determine the full extent of late effects.