Tandem-ring applicator lowers rectal and sigmoid doses compared to tandem-ovoid in cervical cancer patients

PURPOSE: This study compared dosimetry and early clinical outcomes of tandem-ring (T-R) and tandem-ovoid (T-O) applicators in cervical cancer patients treated with computed tomography (CT)-guided volume-based intracavitary brachytherapy (ICBT). METHODS: Between April 2023 and June 2024, 36 eligible patients who completed pelvic external beam radiotherapy (EBRT) were randomized 1:1 to receive CT-guided volume-based ICBT with either T-O (n = 18; 72 applications) or T-R (n = 18; 72 applications). The EBRT consisted of 46 Gy in 23 fractions using 3-dimensional conformal radiotherapy (3DCRT). Brachytherapy was delivered as 28 Gy in 4 fractions (7Gy/fraction), twice weekly. The primary endpoint was rectal D2cc (EQD2), and the secondary endpoints included high-risk clinical target volume (HR-CTV) D90% and D98% (EQD2), bladder and sigmoid D2cc (EQD2), volumetric indices (V95%, V85%, V50%, and V20%), tumor response, and acute toxicity. RESULTS: Mean rectal D2cc (EQD2) was reduced by 2.7 Gy (p = 0.04; 95% CI: 0.1-5.2) with T-R compared to T-O. Sigmoid D2cc decreased by 6.8 Gy (p = 0.005; 95% CI: 2.2-11.4), while bladder D2cc was comparable. HR-CTV D90%, D98%, and volumetric indices (V95%-V20%) were similar across groups. At a median follow-up of 7 months (range, 1-14), early clinical outcomes including complete response and acute GI/GU toxicities did not differ significantly. CONCLUSION: This trial, the first randomized comparison of T-R and T-O applicators, demonstrated that T-R achieved significantly lower rectal and sigmoid doses while maintaining comparable bladder doses, HR-CTV coverage, and early outcomes. Longer follow-up is needed to confirm whether these dosimetric advantages translate to reduced late morbidity.