Space-making Particle Therapy Using Bioabsorbable Spacer for Bone and Soft Tissue Sarcomas: Two-institution Experience.

BACKGROUND/AIM: Particle therapy for bone and soft tissue sarcomas (BSTSs) is limited if the tumor is close to the intestine. Space-making particle therapy (SMPT) using a bioabsorbable spacer (BAS) may treat this condition. We aimed to evaluate SMPT outcomes using a BAS for BSTSs.

PATIENTS AND

METHODS

We retrospectively identified 28 patients who underwent SMPT with BAS between November 2019 and August 2023. Outcomes and associations with each factor were analyzed using the Kaplan-Meier method and log-rank test. Adverse events were determined using CTCAE v5.0.

RESULTS

The median age was 48.5 years (1-78), and the most common histological type was chordoma (25%). Among all patients, 71% were treated with proton therapy and 29% with carbon ion therapy. The most frequent dose fractionations were 70.4 Gy (relative biological effectiveness) in 16 fractions (36%) and 32 fractions (36%). The median follow-up period was 29.5 months (7-48). The 3-year overall survival, progression-free survival, and local control rates were 83%, 63%, and 80%, respectively. Tumor location (pelvis) and low aggressive sarcoma (chordoma and Ewing sarcoma) were significantly associated with better progression-free survival. Adverse events related to the BAS included grade 2 constipation in 7% of patients. Radiation toxicities included acute grade 2 and 3 dermatitis in 36% and 4% of patients, respectively. Late grade 2 toxicities included fractures (7%), peripheral motor neuropathy (4%), dermatitis (4%), superficial soft tissue fibrosis (4%), and skin pain (4%). Late grade 3 toxicities involved fractures (4%).

CONCLUSION

SMPT using a BAS appears effective and safe for treating BSTSs near critical organs, enabling curative dosing with minimal toxicity. Longer follow-up is needed to assess long-term outcomes.