MRI-guided brachytherapy for cervical cancer treatment: The significance of bladder morphology in dose distribution planning

Purpose: This retrospective study aimed to investigate the influence of bladder filling type (BFT) on the relation- ship between bladder volume (BV) and maximum absorbed dose (D 2cc ) in intra-cavitary brachytherapy (ICBT) for cervical cancer. Material and methods: The study enrolled 269 patients who underwent 3D-optimized ICBT guided by MRI scans between 2016 and 2022. Bladder shape (categorized as tilted, curved, or E) was determined based on specific applica- tors used. D 2 cc values were recorded for critical organs, such as bladder, rectum, sigmoid colon, and small bowel. Results: The tilted group exhibited lower D 2 cc values for the small bowel when BV was less than 400 cc, while still ensuring minimal doses to the rectum and sigmoid colon. In the curved group (BV <= 100 cc), significant variations in D 2cc for organs at risk were observed. However, in the E group, no substantial correlation between BV and D 2 cc was identified ( p = -0.035). Additionally, the mean mid-sagittal line differences in the tilted group were 8.47 mm (pre-ICBT) and 7.11 mm (during ICBT simulation), surpassing measurements in the other two groups. Conclusions: This study underscores the substantial impact of bladder shape on both the optimal bladder filling volume and maximum absorbed dose in cervical cancer ICBT. The implementation of BFT based on pre-ICBT MRI scans is both practical and beneficial. It accentuates the necessity of accounting for bladder shape when determining appropriate bladder filling volume, thus facilitating effective management of bladder and small bowel doses. Further prospective studies are warranted to assess the effect of BFT on the incidence of cystitis and proctitis following ICBT, all while maintaining consistent bladder distension.