45 GyRBE for group III orbital embryonal rhabdomyosarcoma.

Purpose: Despite widespread concerns of radiotherapy toxicity in children with head and neck tumors, recent Children's Oncology Group (COG) findings suggest that the use of 45 Gy results in an unacceptably high rate of local recurrences in patients with low-risk orbital rhabdomyosarcoma. We therefore evaluated outcomes in our pediatric patients who received 45 GyRBE using proton therapy. Material and methods: To assess disease control and toxicity, we reviewed the medical records of 30 children (≤21 years old) with COG stage 1, group III embryonal orbital rhabdomyosarcoma enrolled on a prospective outcome study and treated with proton therapy between 2007 and 2018.

Results

Median age at the time of radiation was 4.8 years old. Twenty-one and nine patients received ifosfamide- and cyclophosphamide-based chemotherapy according to their respective cooperative group regimens. Median duration between the start of induction chemotherapy and radiation was 12 weeks. Two patients had a complete response to induction chemotherapy and two had stable disease. Twenty-six patients had a partial response to induction chemotherapy, with a median volume reduction of 66%. With a median follow-up of 4.0 years (range, 0.5-9.5 years), we observed 1 local failure 6 months following treatment in a patient who had a partial response to cyclosphophomide-based induction chemotherapy. The 5-year local control, progression-free survival, and overall survival rates were 97%, 97%, and 100%, respectively. Serious late toxicities included 18 patients with cataracts, 4 with exposure keratoconjunctivitis resulting in permanently reduced visual acuity, and 1 with chronic sinusitis.

Conclusion

45 GyRBE offers effective local control for most patients with group III orbital rhabdomyosarcoma. The delivery of proton therapy to the postinduction tumor volume plus a small margin can mitigate early- and intermediate-term toxicity, but side effects still occur and long-term data are needed to demonstrate the dosimetric advantage of proton therapy.