Proton Radiotherapy Safe and Effective in Pediatric Rhabdomyosarcoma
In a phase II study reported in the Journal of Clinical Oncology, Ladra et al found that proton radiotherapy was a safe and effective treatment in pediatric rhabdomyosarcoma. Proton radiotherapy can substantially reduce radiotherapy doses to normal tissue compared with conventional photon radiotherapy. At the time this study was started, there were three proton radiotherapy centers in the United States, whereas there are now 14, and few data on outcomes with the modality were available.
Study Details
In the study, 57 patients with localized rhabdomyosarcoma aged ≤ 21 years or metastatic embryonal rhabdomyosarcoma aged 2 to 10 years were enrolled between February 2005 and August 2012. Patients received chemotherapy based on vincristine, actinomycin, and either cyclophosphamide or ifosfamide and proton radiation, which was given at Massachusetts General Hospital or MD Anderson Cancer Center. The median proton radiotherapy dose was 50.4 GyRBE (relative biological effectiveness; range = 36–50.4 GyRBE). Surgical resection was based on tumor site and accessibility.
Patients had a median age of 3.5 years (range = 0.6–19.5 years), with 49% aged ≤ 2 years; 53% were female; 74% had intermediate-risk disease; 72% had embryonal histology; and 65% had tumors arising in unfavorable sites. The most common primary sites were parameningeal (47%) and orbital (23%), with intracranial extension in 56% of patients with parameningeal tumors.
Outcomes
Median follow-up was 47 months (range = 14–102 months) for survivors. Among all patients, 5-year event-free survival was 69%, 5-year overall survival was 78%, and the 5-year local control rate was 81%. According to low-risk and intermediate-risk group, 5-year event-free survival was 93% and 61%, 5-year overall survival was 100% and 70%, and 5-year local control was 93% and 77%.
No grade 4 acute or late toxicities were observed. Grade 3 acute toxicity was observed in 11 patients (19%), with the most common being odynophagia (10% of patients with parameningeal or head and neck sites) and dermatitis (9% of all patients). Grade 3 late toxicity was observed in 3 patients (7%), consisting of unilateral cataract (patient with orbital primary), chronic otitis (patient with parameningeal mastoid primary), and retinopathy with decreased visual acuity (patient with orbital primary).
The investigators concluded: “Five-year [local control], [event-free survival], and [overall survival] rates were similar to those observed in comparable trials that used photon radiation. Acute and late toxicity rates were favorable. Proton radiation appears to represent a safe and effective radiation modality for pediatric [rhabdomyosarcoma].”
Torunn I. Yock, MD, MCH, of Massachusetts General Hospital, is the corresponding author for the Journal of Clinical Oncology article.
The study was supported by a Children’s Oncology Group Chair grant and other philanthropic sources (cog-foundation.org). The Children’s Oncology Group is primarily funded by the National Cancer Institute.
Study author Nancy J. Tarbell, MD, reported a consultant or advisory role and stock owndership with ProCure.
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