Definitive particle therapy using protons or carbon ions for dedifferentiated liposarcoma

Background

Particle therapy is effective for the treatment of soft tissue sarcomas. However, the clinical outcomes of definitive particle therapy, particularly for dedifferentiated liposarcoma (DDLS), remain unknown.

Purpose

To analyze the treatment outcomes of proton and carbon ion particle therapies for DDLS.

Methods

We retrospectively included patients with DDLS who were treated with particle therapy between 2008 and 2022. The local control (LC), progression-free survival (PFS), and overall survival (OS) rates were evaluated.

Results

Fifty-seven patients were included in this analysis. The median patient age was 68 years (range, 36–91 years). The most common tumor site was the retroperitoneum (n = 37), with a median gross tumor volume (GTV) of 181 cm³. Twenty-nine patients received proton therapy, and 28 patients received carbon ion therapy. The most common fractionation dose was 70.4 Gy (relative biological effectiveness) in 32 fractions (72.7 Gy equivalent dose in 2 Gy fractions [EQD2]). The median follow-up time was 33 months (range, 1–128 months). The 3-year LC, PFS, and OS rates were 73.1 %, 44.6 %, and 70.6 %, respectively. Patients who received a higher prescribed dose (≥72.7 Gy EQD2) showed significantly better LC (p = 0.04) than did those who received a lower prescribed dose. Moreover, those with a larger GTV (≥181 cm³) had significantly worse OS (p = 0.04) than did those with a smaller GTV. Late adverse events occurred in five (9 %) patients.

Conclusions

Particle therapy using protons or carbon ions for the treatment of DDLS is safe and provides good OS and LC. However, further studies with longer follow-up periods and larger cohorts are warranted.