Impact of bladder volume and bladder shape on radiotherapy consistency and treatment interruption in prostate cancer patients

Abstract Background To investigate the effect of bladder volume (BV) and bladder shape on consistency and treatment interruption in prostate cancer radiotherapy (RT). Methods A total of 275 patients who underwent radical prostate cancer RT in our institution from April 2015 to December 2022 were enrolled. Bladder height, bladder width, and bladder length were defined and recorded. The receiver operating characteristic (ROC) curves were used to evaluate the best cut‐off point for bladder shape. Logistic regression analysis was used to analyze the relationship between setup errors and bladder shapes and BV. Results Based on the ROC curves for 275 patients, the bladder shapes were classified into three: (a) the elongated bladder, (b) the spherical bladder, and (c) the oval bladder. Sixty‐six prostate cancer patients (1611 CBCTs) were randomly selected proportionally. It was found that bladder shape has a greater impact on setup errors than BV (BV: OR = 1.470, p = 0.037; bladder shape: OR = 2.013, p < 0.001), and the setup error of the spherical bladder in anterior–posterior (AP) direction was greater than the others ( p < 0.001). In addition, the shape consistency of the spherical bladder was the worst (43.0%) during RT. Compared with the inconsistent group, the group with the same bladder shape had higher consistency in BV (CBCT/CT) ( p < 0.001), and a smaller setup error in the AP direction ( p < 0.001). Similarly, the treatment interruption fractions were highest in spherical bladder RT. Conclusions More specific bladder filling requirements should be developed for different bladder shapes. More attention should be paid to the spherical bladder for precise RT.