Development and assessment of interstitial brachytherapy using individual curved-needle in treatment of recurrent gynecological tumors after external beam radiotherapy

Objective: To evaluate the efficacy and safety of individualized curved-needle interstitial brachytherapy (ISBT) using 3D printing for recurrent gynecologic tumors. Method: This study enrolled patients with pelvic recurrent gynecologic tumors from March 2022 to April 2024. All patients received external beam radiotherapy (EBRT) (40-60 Gy, 20-30 fractions), followed by individualized curved-needle ISBT using a 3D-printed applicator (12-30 Gy, 2-5 fractions). Concurrent systemic therapy was administered when necessary. Dosimetric parameters (V100%, V200%, D100%, D98%, D90%, D50%, D5cc, D2cc, D0.1cc) were assessed. Clinical outcomes and treatment-related complications were analyzed. Results: 45 fractions of ISBT were analyzed. Central and non-central pelvic recurrences occurred in 46.2% and 53.8% of patients, respectively. Eight patients received concurrent systemic therapy. The cumulative equivalent dose to the gross tumor volume of recurrence treatment was 64.87 ± 7.16 Gy for patients with prior radiation and 73.03 ± 9.95 Gy for others. The cumulative equivalent dose to D2cc in brachytherapy for patients with vs. without prior radiation was 19.75 ± 8.92 Gy vs. 21.65 ± 9.49 Gy for the bladder, 13.23 ± 2.81 Gy vs. 15.25 ± 6.82 Gy for the rectum, and 9.09 ± 5.85 Gy vs. 8.23 ± 5.09 Gy for the sigmoid colon. At a median follow-up of 25 months, 100% of patients were alive. The objective response rate was 84.6%, with 91.7% local control at 2 years. Acute Grade 3 toxicity was observed in 30.8%, and late Grade 3 toxicity in 7.7%. Conclusion: Individualized curved-needle ISBT with a 3D-printed applicator provides high-quality treatment for recurrent gynecologic tumors with favorable outcomes and acceptable toxicity.