Effect of Bladder and Rectum Volume Standardization on Interfractional Dose in Intracavitary (Intrauterine + Paracervical) Brachytherapy of Cervical Cancer

Purpose: This study evaluated the effect of interfractional bladder and rectum filling on HRCTV and OAR (bladder, rectum, sigmoid) doses in intracavitary brachytherapy for cervical cancer. Methodology: A retrospective analysis was conducted on CT-simulation images of 25 patients (12 treated with T+O and 13 with T+R applicators). Patients were placed in the dorsal lithotomy position under sedation. A Foley catheter balloon was inflated with 7 cc contrast and the bladder filled with 120 cc of contrast-saline, then clamped. After uterine canal measurement, a suitable T+R or T+O applicator was inserted and fixed by the radiation oncologist. For each patient, new CT-sim images were acquired in the second fraction, and new treatment plans were generated. Dose-volume histograms (DVHs) were analyzed to determine HRCTV (D100, D90) and OAR doses (2cc, 1cc, 0.1cc). Dose variations between fractions were evaluated. Findings and Conclusion: For the T+O applicator, median HRCTV volumes were 30.76 ± 13.05 cc (first fraction) and 29.24 ± 12.91 cc (second fraction). Bladder, rectum, and sigmoid volumes in the second fraction were 151.38 ± 81.28 cc, 56.94 ± 28.44 cc, and 42.89 ± 33.46 cc, respectively. No significant differences were observed in target or OAR volumes or doses between fractions for either applicator type. Consequently, interfractional organ motion did not significantly affect dose distribution. Therefore, when bladder and rectum volume standardization is achieved, the first fraction plan can be safely used for subsequent treatments.