Interstitial brachytherapy in soft tissue sarcoma: a 5 years institutional experience with Cobalt 60- based high-dose-rate brachytherapy system

Purpose
Soft tissue sarcoma (STS) is rare but aggressive neoplasm. Interstitial brachytherapy (ISBT) alone or combined with external beam radiotherapy (EBRT) as post-operative treatment improves loco-regional (LRC) and distant control.

Material and methods
Out of twenty-nine non-metastatic STS (lower limb 64%) patients (median age 37 yrs), treated with surgery and post-operative ISBT during February 2011 – December 2016, 27 patients with > 6 months follow-up were analyzed. Spindle cell sarcoma was the commonest (24%) histology. Eleven patients (44%) received EBRT (45-50 Gy), where ISBT was used as boost (16-20 Gy). Fourteen patients (56%) received ISBT alone (4 Gy per fractio). Treatment was done with a 60 Cobalt (60Co) source high-dose-rate system.

Results
With a median follow-up of 20 months (17-51 months), LRC rate was 85.7% (with EBRT 90.5% and ISBT 83.2% alone). Median disease-free survival (DFS) was 39.7 ±3.9 months (32-47.2 months). Median loco-regional failure-free survival (LRRFS) was 43.8 ±3.6 months (36.8-50.9 months). Distant failure-free survival (DFFS) was 18 months (15.5-26.6 months). Overall survival was 42.4 ±3.4 months (35.7-48.1 months). Tumor grade was a significant factor for DFFS. Total radiation dose (including EBRT) has significant influence on DFS and LRRFS. 14.8% patients developed ≥ grade 2 late toxicity (skin atrophy, hypo-pigmentation, and telangiectasia).

Conclusions
Combination of surgery and ISBT with/out EBRT improves local and distant control with acceptable late toxicities. 60Co-based ISBT is safe and gives a good outcome.