3619 - Cesium-131 Brachytherapy vs. SBRT for Frail Patients with Head and Neck Cancers Not Eligible for Conventional External Beam Radiation Therapy

Purpose/Objective(s): Frail, elderly, and previously irradiated patients with advanced head and neck cancers (HNC) are frequently ineligible for conventional external beam radiation therapy (EBRT), creating a major therapeutic gap. We report outcomes from an ongoing prospective study of intraoperative Cesium-131 (Cs-131) brachytherapy following gross total resection and compare results with a contemporary SBRT (stereotactic Body Radiation therapy) cohort treated under similar ineligibility criteria.

Materials/Methods: This IRB-approved prospective study enrolled operable advanced HNC patients typically requiring post-operative EBRT but ineligible due to prior full-course radiation, poor performance status, or patient preference. Following resection, Cs-131 seeds were implanted intraoperatively into the tumor bed (1-cm spacing; median dose 70 Gy, range 70–80 Gy). Patients were followed every 2–4 months in year one, then every 3–6 months. Toxicity was graded per CTCAE v5.0. Local control (LC) was defined as recurrence within 0.5 cm of the implant site. A retrospective SBRT cohort (2018–2024) meeting similar criteria was analyzed. Groups were compared using chi-square/Fisher’s exact tests and t-test/Mann-Whitney tests. Overall survival (OS) was estimated via Kaplan-Meier and compared using log-rank testing. Hazard ratios (HR) with 95% confidence intervals (CI) were calculated.

Results: Significant differences between Cs-131 and SBRT cohorts were observed in primary site (p<0.001), overall toxicity (p<0.001), toxicity grade (p<0.001), and disease status (p=0.002). Within the SBRT cohort, toxicity grade was not associated with site, HPV status, or PTV volume. OS did not differ significantly (p=0.0942); however, SBRT demonstrated a higher hazard of death (HR 2.05; 95% CI: 0.84–5.02). Median OS for SBRT was 11.5 months (95% CI: 7–20); median OS was not reached for Cs-131.

Conclusion: In medically fragile HNC patients ineligible for EBRT, intraoperative Cs-131 achieved comparable survival with significantly reduced toxicity versus SBRT. Prospective randomized evaluation is warranted.