Long-term outcomes, prognostic factors, and patterns of failure of postoperative adjuvant iodine-125 seed brachytherapy for parotid carcinoma: a large single-institution cohort.

BACKGROUND

Evidence supporting postoperative iodine-125 (125I) seed brachytherapy for parotid carcinoma remains limited. This study evaluated its long-term efficacy, safety, and prognostic factors in a large single-institution cohort.

METHODS

We retrospectively analyzed 828 patients with primary or recurrent parotid carcinoma treated with surgery followed by adjuvant 125I seed brachytherapy between 2002 and 2020. Overall survival (OS), disease-free survival (DFS), and locoregional recurrence-free survival (LRFS) were estimated using Kaplan-Meier analysis, and prognostic factors were identified using Cox regression.

RESULTS

With a median follow-up of 104.7 months, the 5-year OS, DFS, and LRFS rates were 87.0%, 76.6%, and 84.7%, respectively. Multivariable analysis revealed that advanced age (≥60 years), T3/4 stage, nodal positivity, recurrent disease, high-risk histology, perineural invasion, and positive/gross residual surgical margins (R1/R2) were independent predictors of worse OS. Additionally, an interval from surgery to brachytherapy exceeding 6 weeks significantly predicted poorer DFS and LRFS. Locoregional recurrence was the primary failure pattern (53.9% of failures), though 64.3% of recurrent patients survived at 3 years following salvage. Late toxicities occurred in 18.4% of patients.

CONCLUSIONS

Postoperative adjuvant 125I seed brachytherapy provides durable long-term locoregional control with acceptable toxicity. These findings support its role in risk-adapted management, emphasizing the importance of surgical margin status and timely initiation of adjuvant treatment.