Intensity Modulated Carbon Ion Radiation Therapy Using Pencil Beam Scanning Technology for Patients With Unresectable Sacrococcygeal Chordoma

Abstract

ObjectivesTo investigate the safety and efficacy of intensity modulated carbon ion radiotherapy (IM-CIRT) using pencil beam scanning technology for patients with unresectable sacrococcygeal chordoma (SC). Methods and MaterialsA total of 35 unresectable SC patients were retrospectively analyzed, including 54.3% (19/35) recurrent cases. 68.6% (24/35) cases’ tumor located in S2 or above, and all cases were treated with hypofractionated IM-CIRT. The median dose was 70.4 (range 69 - 80) Gy (RBE) in 16 (range 16 - 23) fractions, typically delivered over 5 fractions per week. ResultsThe 3-year OS, CSS, PFS, LRFS and DMFS rates with a median follow-up time of 42 (12∼91) months for the entire cohort were 93.2%, 96.3%, 61.8%, 80% and 77.3%, respectively. Multivariate analysis revealed that GTV volume (HR, 3.807; 95% CI: 1.044 - 13.887, p = 0.043) was the only significant prognostic factor for PFS and the dose for the GTV ≥ 70.4 Gy (RBE) was relevant with significantly better LRFS (HR, 0.190; 95% CI: 0.038 – 0.940, p = 0.042). No significant prognostic factor for OS, CSS and DMFS and no severe (i.e., grade ≥ 3) acute toxicity were identified. Severe late toxicities occurred in 3 patients (8.57 %): pain (1 patient), motor neuropathy (1 patient) and skin ulcer (1 patient). Furthermore, no severe toxicity related to urinary function or defecation was observed following IM-CIRT. Pain grades improved or remained unchanged in 85.7% of patients. ConclusionIM-CIRT produced acceptable 3-year outcomes without substantial late adverse effects, especially urinary and anorectal complications for SC, and did not appear to increase pain. IM-CIRT at high doses using hypofractionated RT may improve outcomes for local control and seems to be feasible even for postoperative recurrent SC.