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Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Proton Beam Therapy in Nonmetastatic Rhabdomyosarcoma: Outcome, Prognostic Factors, and the Effect of Timing of
Mohamed Mortada Elsharief1, Shermaine Pan2, Yuwei Wang2
1The Christie NHS Foundation Trust, Manchester, United Kingdom; Department of Radiation Oncology, National Cancer Institute, Cairo University, Giza, Egypt.
Purpose:
We report survival and disease-specific outcomes, prognostic factors, and the impact of radiation therapy timing in patients with nonmetastatic rhabdomyosarcoma (RMS) treated with definitive proton beam therapy (PBT) at a national UK center.
Methods And Materials:
We retrospectively reviewed patients with nonmetastatic, pathologically confirmed RMS treated with definitive PBT at the Christie Proton Beam Therapy Centre between December 2018 and May 2025. All patients were treated according to the RMS 2005 or FaR-RMS protocols. Time-to-event outcomes included local control, disease-free survival (DFS), distant metastasis-free survival), and overall survival (OS). Kaplan-Meier methods were used for survival estimates. Prognostic factors were assessed using Firth-penalized Cox regression due to limited event numbers. Multivariable models adjusted for dominant prognostic variables.
Results:
Eighty-four patients were included with a median age of 7.6 years (range, 1-70). Parameningeal primaries accounted for 51% of cases, and 75% of patients had high or very high-risk disease. Median time from chemotherapy initiation to PBT was 13 weeks (range, 10-22). After a median follow-up of 48 months, 4-year OS, DFS, local control, and distant metastasis-free survival were 81.2%, 70.8%, 75.4%, and 89.7%, respectively. Fifteen patients developed local failure, all occurring in-field within the high-dose region. On univariate analysis, parameningeal primary site and advanced T stage (T3-4) were significantly associated with inferior OS and DFS. Radiation therapy initiation at ≥14 weeks was not independently associated with worse outcomes after adjustment for other variables. Within the parameningeal subgroup, intracranial extension was associated with significantly inferior OS.
Conclusions:
Definitive PBT for nonmetastatic RMS resulted in disease control and survival outcomes comparable to those reported in cooperative group trials and other proton therapy series. Prognosis appears to be primarily driven by disease-related factors, particularly parameningeal location, intracranial extension, and advanced T stage. Radiation therapy timing was not independently associated with outcomes after adjustment for these factors; however, these findings should be interpreted with caution, particularly in relation to DFS. Further validation in larger, multi-institutional data sets is warranted.
