Multi-Institutional Experience of Proton Therapy for Rhabdomyosarcoma and Ewing Sarcoma in the Proton Collaborative Group (PCG) Prospective Registry

PURPOSE/OBJECTIVE(S)

To report on outcomes, acute toxicities, and the use of dose-escalation with proton therapy (PT) in patients with rhabdomyosarcoma and Ewing sarcoma in a prospective multi-institutional registry (PCG).

MATERIALS/METHODS

Data on patients with primary rhabdomyosarcoma and Ewing sarcoma treated with definitive PT (defined as ≥45 Gy) were queried from the PCG registry. A similar query was performed of our institutional database with IRB approval. Overall survival rates were calculated by Kaplan-Meier. Toxicities were scored using CTCAE v4.0.

RESULTS

A total of 354 patients across 10 institutions (203 rhabdomyosarcoma, 151 Ewing sarcoma) met the eligibility criteria. Median age was 9 years (Interquartile Range: 5-15). Median dose was 50.4 GyRBE for rhabdomyosarcoma patients (Range: 45-66 GyRBE) and 55.8 GyRBE for Ewing sarcoma patients (Range: 45-66 GyRBE). Median follow-up was 2.4 years (Range 0.3-12.3 years). Two-year overall survival rates were 81.1% (95% CI: 73.7%-88.5%) for rhabdomyosarcoma and 79.1% (95% CI: 71.7%-86.2%) for Ewing sarcoma. The Table lists the prescription doses delivered by tumor histology; 28.1% of rhabdomyosarcoma and 21.9% of Ewing sarcoma patients, respectively, received dose-escalated radiotherapy (defined as >50.4 Gy for rhabdomyosarcoma and >55.8 Gy for Ewing sarcoma). Excluding alopecia and skin desquamation, 153 patients (43.2%) developed any acute grade 2+ non-hematologic toxicity, while 49 patients (13.8%) developed one or more grade 3 toxicities. The most common grade 3 toxicities were anorexia/weight loss (7.3%), pain (7.3%) mucositis/esophagitis (4.8%), and nausea/vomiting (3.1%). One grade 4 toxicity (esophagitis) and no deaths were reported during treatment.

CONCLUSION

In this multi-institutional prospective registry, 28.1% of rhabdomyosarcoma and 21.9% of Ewing sarcoma patients received dose-escalated PT, with 13.8% of patients developing grade 3 toxicities. Long-term outcomes for disease control and late toxicity and anticipated cooperative group trial results are needed to fully assess the benefits and risks of dose-escalated radiotherapy for these tumors.

Multi-Institutional Experience of Proton Therapy for Osteosarcoma in the Proton Collaborative Group (PCG) Prospective Registry

PURPOSE/OBJECTIVE(S)

To report on the utilization of dose-escalated radiotherapy, acute toxicities, and survival following definitive proton therapy (PT) for osteosarcoma patients in a prospective multi-institutional study.

MATERIALS/METHODS

Data on patients with osteosarcoma treated with definitive intent PT were queried from the Proton Collaborative Group (PCG) prospective registry. A similar query was performed on an institutional database with IRB approval. Overall survival rates were calculated by Kaplan-Meier. Toxicities were scored using CTCAE v4.0.

RESULTS

Forty osteosarcoma patients across 9 institutions received definitive intent PT between 2011-2021 and met the eligibility criteria. Median age was 32 years (Range: 6-86 years). Median PT dose was 66.6 GyRBE (Range: 50.4-80.0 GyRBE); 38 patients received proton therapy alone, whereas 2 received combined proton/photon therapy. Seventeen (42.5%) patients received doses ≥70 GyRBE. Median follow-up was 3.1 years (Range: 0.9-10.5 years). One-year and three-year overall survival rates were 83.5% and 59.1%, respectively, with 14 deaths due to disease. Excluding skin desquamation and alopecia, 22 patients (55.0%) developed any acute grade 2+ toxicity, and 5 patients (12.5%) developed any grade 3 toxicities. No acute grade 4-5 toxicities were reported. The most frequent grade 2+ non-skin toxicities were fatigue (37.5%), anorexia/weight loss (17.5%), mucositis/esophagitis (22.5%), pain (20.0%), and nausea/vomiting (10.0%). The most frequent grade 3 toxicities were anorexia/weight loss (5.0%), mucositis/esophagitis (5.0%), and neurologic symptoms (5.0%).

CONCLUSION

In this multi-institutional study, 42.5% of osteosarcoma patients treated with PT received doses between 70-80 Gy, with 12.5% experiencing any grade 3 toxicity. Long-term outcomes for disease control, late toxicity, and quality-of-life are needed to more fully assess the benefits and risks of dose-escalated radiotherapy in this radioresistant tumor. The authors plan to assess the outcomes of osteosarcoma patients treated with dose-escalated radiotherapy for unresectable or gross residual disease in future studies.