Dosimetric analysis of the effects of the bladder volume on Organs at Risk (OARs) in high-dose-rate intracavitary brachytherapy in locally advanced carcinoma cervix (Stage IB3, IIA2, IIB–IVA)

Background: Cervical cancer remains a major cause of morbidity and mortality world-wide, particularly in low- and middle-income countries. Intracavitary brachytherapy is integral to definitive treatment but exposes adjacent organs at risk (OARs) to potentially harmful radiation doses. The influence of bladder volume on dosimetry remains controversial. Methods: This retrospective study included 90 patients with Federation of Gynecology and Obstetrics (FIGO) 2018 stage IB3–IVA cervical carcinoma, treated at Ahsania Mission Cancer and General Hospital, Dhaka (2019–2020). Patients were stratified into three groups based on bladder volume: Group A (0–40 cc), Group B (41–80 cc), and Group C (81–120 cc). All received standard chemoradiation followed by High-Dose-Rate (HDR) intracavitary brachytherapy. Dosimetric parameters (D2cc Equivalent Dose in 2 Gy fractions (EQD2) for bladder, rectum, and sigmoid) and High-Risk Clinical Target Volume (HR-CTV) D90 coverage were analyzed. Early response at 6–8 weeks was also assessed. Results: Mean bladder D2cc was 85.6 Gy (Group A), 73.2 Gy (Group B), and 78.9 Gy (Group C), with Group B significantly lower (p = 0.002). Rectal D2cc followed a similar trend (70.2 Gy, 64.5 Gy, and 72.4 Gy; p = 0.01). Sigmoid D2cc showed no significant variation (p = 0.41). HR-CTV D90 remained comparable across groups (82.8–84.2 Gy; p = 0.48). Complete response was achieved in 73.3% of patients, with no significant difference between groups (p = 0.57). Conclusions: A moderately filled bladder (∼60 cc) provides the most favorable dosimetric profile, significantly reducing bladder and rectal doses while maintaining adequate tumor coverage. Standardizing bladder filling protocols may enhance treatment safety and consistency in HDR brachytherapy for cervical cancer.