Particle Therapy in Adult Patients with Pelvic Ewing Sarcoma—Tumor and Treatment Characteristics and Early Clinical Outcomes

SIMPLE SUMMARY: Radiotherapy is a crucial component in the multimodal treatment of Ewing sarcoma; it can be applied for local disease in addition to surgery or as definitive treatment for inoperable disease. Particularly in pelvic Ewing sarcoma, definitive radiotherapy offers the possibility of avoiding extensive and potentially mutilating resections and preserving crucial neurological functions. Adult patients with primary or locally recurrent pelvic Ewing sarcoma treated with curative intent with protons for primary disease and carbon ions for recurrent disease at the Heidelberg Ion-Beam Therapy Center (HIT) were considered for this retrospective analysis. We report excellent dosimetric characteristics in the treatment with protons in comparison to photon IMRT and promising early clinical outcomes. Particle therapy in adult pelvic Ewing sarcoma is shown to be feasible in a consecutive patient cohort. However, further long-term follow-up is needed to assess late toxicity and clinical outcomes. ABSTRACT: Purpose: To report dosimetric characteristics and early clinical outcomes in patients with pelvic Ewing sarcoma undergoing particle therapy. Methods: Patients ≥ 18 years old with pelvic Ewing sarcoma treated in adjuvant or definitive settings were considered for this retrospective analysis. Proton therapy was carried out with 45–60 Gy (RBE) (1.5–2 Gy (RBE) per fraction) and carbon ion therapy for recurrent disease with 51 Gy (RBE) (3 Gy (RBE) per fraction). Local control (LC), disease control (DC) and overall survival (OS) were calculated using the Kaplan–Meier method. Results: For our sample, 21 patients were available, 18 of whom were treated for primary, 3 for locally recurrent and 16 for inoperable disease. The median CTV and PTV were 1215 cm(3) and 1630 cm(3). Median Dmean values for the PTV, bladder and rectum and median V40 Gy for the bowel for patients undergoing proton therapy were 56 Gy (RBE), 0.6 Gy (RBE), 9 Gy (RBE) and 15 cm(3), respectively. At the end of particle therapy, G 1–2 skin reactions (n = 16/21) and fatigue (n = 9/21) were the main reported symptoms. After a median follow-up of 21 months, the 2-year LC, DC and OS were 76%, 56% and 86%, respectively. Conclusions: Particle therapy in adult pelvic Ewing sarcoma is feasible and provides excellent dosimetric results. First clinical outcomes are promising; however, further long-term follow-up is needed.