Outcomes Following Proton Therapy for Group III Pelvic Rhabdomyosarcoma.

Area of Science:

• Pediatric Oncology
• Radiation Oncology
• Medical Physics

Background:

• Rhabdomyosarcoma (RMS) is a rare pediatric cancer.
• Pelvic RMS presents unique treatment challenges due to proximity to vital organs.
• Proton therapy offers a more targeted radiation approach compared to traditional photon therapy.

Purpose of the Study:

• To evaluate the institutional outcomes of proton therapy for pediatric pelvic rhabdomyosarcoma (RMS).
• To assess local control, progression-free survival, and overall survival rates.
• To analyze treatment-related toxicities and functional outcomes, particularly bladder preservation.

Main Methods:

• A prospective outcome study included 31 children (≤21 years) with group III pelvic RMS treated between 2007-2018.
• Patients received multi-agent chemotherapy followed by proton therapy (median dose 50.4 Gy RBE).
• Surgical interventions, including resection and cystectomy, were analyzed alongside outcomes.

Main Results:

• Five-year local control, progression-free survival, and overall survival rates were 83%, 80%, and 84%, respectively.
• Younger patients (<3 years) demonstrated significantly better local control (100% vs 68%, P=.02).
• Embryonal histology was associated with improved survival (96% vs 54%, P=.02); urinary toxicity was minimal except after cystectomy.

Conclusions:

• Proton therapy for pediatric pelvic RMS yields comparable local control to historical data with reduced toxicity.
• Functional bladder preservation is achievable in a majority of patients.
• Caution is advised for exploratory biopsies within 18 months post-radiation due to potential toxicity.