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

Purpose

To investigate the safety and efficacy of intensity modulated carbon ion radiation therapy (IM-CIRT) using pencil beam scanning technology for patients with unresectable sacrococcygeal chordoma (SC).

Methods and Materials

A total of 35 patients with unresectable SC were retrospectively analyzed, including 54.3% (19/35) recurrent cases. In 68.6% (24/35) cases, tumor was located in S2 or above, and all cases were treated with hypofractionated IM-CIRT. The median dose was 70.4 Gy (range, 69-80 Gy) (relative biologic effectiveness) in 16 fractions (range, 16-23 fractions), typically delivered over 5 fractions per week.

Results

The 3-year overall survival, cause-specific survival, progression-free survival, locoregional progression–free survival, and distant metastasis–free survival rates with a median follow-up time of 42 months (range, 12-91 months) for the entire cohort were 93.2%, 96.3%, 61.8%, 80%, and 77.3%, respectively. Multivariate analysis revealed that gross tumor volume (hazard ratio, 3.807; 95% CI, 1.044-13.887; P = .043) was the only significant prognostic factor for progression-free survival and the dose for the gross tumor volume ≥70.4 Gy (relative biologic effectiveness) was relevant with significantly better locoregional progression–free survival (hazard ratio, 0.190; 95% CI, 0.038-0.940; P = .042). No significant prognostic factor for overall survival, cause-specific survival, and distant metastasis–free survival and no severe (ie, 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.

Conclusions

IM-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 radiation therapy may improve outcomes for local control and seems to be feasible even for postoperative recurrent SC.