Impact of bladder volume precision control on setup errors and dosimetry in intensity-modulated radiation therapy for cervical cancer.

BACKGROUND: Cervical cancer is the most common gynecologic malignancy and a leading threat to women’s health. Intensity-modulated radiation therapy (IMRT) is a cornerstone treatment, but its success depends on precise patient positioning and consistent bladder distension to minimize setup errors and organ motion. This study evaluated the impact of bladder volume variation on setup errors during IMRT and the accuracy and clinical utility of a bladder volume scanner (BVS) for bladder volume management. METHODS: We conducted a prospective, allocated comparative study of 62 cervical cancer patients treated with IMRT between April 2021 and August 2022. Patients were allocated to a BVS group (n = 31) that used a bladder scanner to maintain a target bladder volume of 250–350 mL (± 30 mL) or to a control group (n = 31) that relied on a strong urge to urinate for bladder filling. We compared bladder volume consistency, setup errors in left-right (X), anterior-posterior (Y), and superior-inferior (Z) directions, homogeneity and conformity indices, and the volumes of bladder, rectum, and small intestine receiving 45 Gy between groups. We also analyzed the correlation between bladder volume measured by BVS and by computed tomography (CT). RESULTS: The BVS group had significantly more consistent bladder volumes and significantly smaller setup errors in all directions than the control group. The median (interquartile range, IQR) setup errors in the BVS vs. control group were 1.0 (0.8–1.5) vs. 1.7 (1.2–2.5) mm in the X-axis, 0.4 (0.2–1.1) vs. 1.9 (1.5-3.0) mm in the Y-axis, and 1.1 (0.9–1.3) vs. 2.8 (2.0-3.5) mm in the Z-axis, respectively (all P < 0.01). The BVS group also showed improved dosimetry, with a better homogeneity index (1.01 vs. 1.11) and conformity index (0.98 vs. 0.94), and significantly lower bladder, rectum, and small intestine volumes receiving 45 Gy (24.6% vs. 29.1%, 19.7% vs. 25.3%, and 17.4% vs. 18.1%, respectively; all P < 0.01). Bladder volumes measured by the scanner were strongly correlated with CT-derived volumes (R = 0.977). CONCLUSIONS: Precise bladder volume control using a BVS leads to more reproducible patient positioning, as evidenced by significantly reduced bony anatomy-based setup errors, and resulted in significantly reduced radiation exposure to adjacent organs. The strong correlation between BVS and CT measurements confirms the device’s reliability. By ensuring a reproducible daily anatomical setup, BVS-guided bladder management improves the precision of IMRT delivery. This approach mitigates a key source of treatment uncertainty and establishes a foundation for potentially safer margin reduction or dose escalation strategies in the future. The bladder scanner was highly accurate and reproducible, improving target delineation and potentially allowing safer dose escalation.