2385 - Proton Therapy for Pediatric Patients with Localized Unresectable Osteosarcoma
Presenter(s)
D. J. Indelicato1, J. A. Bradley2, A. Spiguel3, A. B. Collier III4, C. G. Morris2, and R. Mailhot Vega2; 1Department of Radiation Oncology, University of Florida, Jacksonville, FL, 2Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, 3Department of Orthopaedic Surgery and Sports Medicine, University of Florida College of Medicine, Gainesville, FL, 4Division of Pediatric Hematology, Nemours Children’s Health, Jacksonville, FL
Purpose/Objective(s): Unresectable osteosarcoma requires high doses of radiation for local control (LC). In theory, these tumors are well-suited for proton therapy (PT), particularly in young patients with non-metastatic disease who are at risk of serious long-term toxicity from radiation doses >70 Gy relative biological equivalent (RBE).
Materials/Methods: Between 2006 and 2024, 9 patients with a median age of 17.4 years (range, 9.6 – 21.9) received PT for non-metastatic osteosarcoma. Six patients had tumors of the pelvis and three of the skull base/cervical spine. All patients had unresectable gross disease at the time of treatment: 7 patients had biopsy prior to radiation and 2 patients had multiple operations to debulk the tumor. All received contemporary osteosarcoma chemotherapy regimens including cisplatin, doxorubicin, and high dose methotrexate prior to radiation. All patients were prescribed a dose of 70.2 GyRBE at 1.8 GyRBE/fraction daily. Seven patients were treated with double-scattered (DS) and 2 with pencil beam PT. The two patients with titanium rod stabilization received DS PT with a minority element of volumetric arc photon therapy (VMAT) based photon therapy. Two patients stopped treatment early: one due to acute toxicity (mucositis) after 43.2 GyRBE and another with local disease progression after 55.8 GyRBE.
Results: The median actual follow-up is 1.8 years (range, 0.4 – 7.3) and the median potential follow-up is 7.6 years (range, 3 – 14.2). No patients were lost to follow-up. The 5-year overall survival, progression-free survival, and LC were 33%, 22%, and 44%, respectively. Only 2 patients remain alive and free of disease, both with primary tumors of the cervical spine treated with DS + VMAT. One of these was the patient who stopped PT early due to mucositis. The other finished PT but developed mucositis that contributed to dehydration resulting in acute renal failure and Fanconi syndrome. This was followed by severe esophageal stricture requiring total colonic transposition to replace the esophagus.
Conclusion: This is the first report on the efficacy and toxicity of PT in pediatric patients with osteosarcoma. Despite the dosimetric advantage of PT compared to photons, the therapeutic ratio remains unsatisfactory, with poor disease control and major toxicity in survivors.