Two Decades of Outcomes and Quality of Life Following Pencil Beam Scanning Proton Therapy in Children and Adolescents with Rhabdomyosarcoma

Abstract

Background: RMS is the most common soft tissue sarcoma in children. Pencil beam scanning proton therapy (PBS PT) enables highly conformal dose delivery with reduced exposure to surrounding healthy structures, making it particularly suited for RMS in critical anatomical regions. Long-term clinical outcome data for this new radiation technique are scarce. Purpose: This study reports long-term outcomes and quality of life after PBS PT in children and adolescents with rhabdomyosarcoma (RMS). Methods and Materials: We retrospectively reviewed 114 children and adolescents with RMS (mostly embryonal, n = 100; 87.7%) treated between 2000 and 2020. Their median age was 4.6 years (range, 0.3–18). All received systemic chemotherapy according to prospective protocols. The median total PT dose delivered was 52 Gy (RBE; range, 41.4–64.8). Results: After a median follow-up period of 7.1 years (range, 0.3 to 17 years), we observed 26 failures overall; 21 (80.8%) occurred in-field. The 5-year local control and overall survival were 81.2% and 81%, respectively. The composite endpoint (non-ocular grade ≥3 toxicity- and failure-free survival) counting the first occurrence of any failure (local or distant), death, or non-ocular CTCAE v5.0 grade ≥3 toxicity was 77.3% at 5 years. At the start of PT, parents and children reported a quality of life significantly worse than that of a German normative group, but during the follow-up period, their scores improved to normal values in nearly all domains within two years. Conclusions: Our two decades of experience with PBS PT provide data that reflect good local control rates and minimal late non-ocular grade 3 toxicity. We also show that quality of life returned to normal scores in nearly all domains within 2 years. Children and adolescents with RMS seem to benefit from PBS PT in terms of toxicity and quality of life, but further prospective, multi-institutional comparative trials are needed.