ESTRO 2025 - Abstract Book

S1726

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

4123

Mini-Oral high-dose carbon ion reirradiation for recurrent sacral chordoma

Agnieszka Chalaszczyk 1 , Maria Rosaria Fiore 1 , Marco Rotondi 1 , Elettra Dorotea Ferrari 2 , Amelia Barcellini 1,3 , Viviana Vitolo 1 , Silvia Molinelli 4 , Alessia Bazani 4 , Giulia Sellaro 5 , Matteo Pepa 5 , Giulia Fontana 1 , Sara Scardo 1 , Ester Orlandi 1,6 1 Clinical Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 2 Department of Radiotherapy, University of Milan, Milan, Italy. 3 Department of Internal Medicine and Therapeutics, University of Pavia, Pavia, Italy. 4 Medical Physics Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 5 Bioengineering Department, CNAO National Center for Oncological Hadrontherapy, Pavia, Italy. 6 Department of Clinical, Surgical, Diagnostic, and Pediatric Sciences, University of Pavia, Pavia, Italy Aims : To evaluate the feasibility of carbon ion re-irradiation (CIR) for recurrent sacral chordoma. The analysis focused on in-field progression-free survival (IPFS), overall survival (OS), and late toxicity, assessed retrospectively. Materials and methods: Between February 2015 and September 2023, 33 patients with recurrent sacral chordoma, previously treated with photon, proton, or carbon ion radiotherapy (RT), underwent CIR. IPFS and OS were estimated using the Kaplan Meier method. Late toxicity was assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Results : The median follow-up after CIR was 32.17 months (range, 5.23 – 96.83 months). Recurrences following previous RT were observed in-field in 15 patients, marginal in 14 patients, and out-field in 4 patients. The median interval between RT courses was 29.4 months (range, 6.07-111.57). All patients received CIR with a median total dose of 60 Gy (relative biological effectiveness [RBE]; range, 45-70.4 Gy [RBE]) with a median dose per fraction of 4 Gy [RBE] (range, 3-4.8 Gy [RBE]). The total dose was approved based on the cumulative plans, considering maximum dose not exceeding 140 Gy [RBE] within the overlap region. The 2-year and 3-year IPFS rates were 50% and 29%, respectively, while the 2-year and 3-year OS rates were 91% and 87%, respectively. Grade 3 late toxicities included skin ulceration in one patient and motor-sensory neuropathy in two patients. Seven patients underwent a second course of CIR with a median total dose of 57 Gy [RBE] (range, 48 – 70.4 Gy [RBE]); this included 4 cases of marginal recurrence and 3 cases of out-field recurrence. After a median follow-up of 30.8 months (range, 24.67 – 36.43 months) following the second CIR, there was one case of infield progression and two cases of marginal progression.The remaining four patients were stable at the time of the last follow-up. Conclusions : Despite the inherent challenges of re-irradiation, our findings suggest that CIR is a feasible and effective treatment for locally recurrent sacral chordoma, with an acceptable toxicity profile. CIR offers a promising alternative to surgical salvage in carefully selected patients.

Keywords: chordoma, reirradiation, CIRT