The association of the uterine motion with bladder volume during radiotherapy in gynecological malignancies

Aim: This study was performed to assess the extent of interfraction uterine motion during radiotherapy for cervical cancer and uterine body carcinoma while maintaining a strict bladder filling protocol. Methods: Twenty-four patients with cervical cancer or uterine body carcinoma who were treated on a linear accelerator, were recruited. During the course of external beam radiotherapy, cone beam computed tomographic scans were taken, once at the start of treatment and then weekly until the completion of the radiotherapy course. Patients were instructed to maintain a strict bladder filling protocol. After negating the effect of patient’s setup error by offline cone beam computed tomographic imaging, the position of the uterus was defined in the clinical target volume. Then the position of the uterus was compared in the following weekly scans. The position of the uterus was also correlated with the position and the filling of the bladder. This change in uterus position was measured separately in the anterioposterior (AP), superioinferior (SI), and lateral directions. Results: According to calculations based on weekly imaging, The mean values of shift in AP, SI, and lateral directions were respectively 0.67, 0.29, and 0.23 The mean extent of motion in the uterine position on a daily basis for individual patients ranged from -2.28 to +1.3 in AP, -0.56 to +0.71 in SI, and from -0.6 to +0.45 in lateral directions. Conclusion: At least once a week cone beam computed tomography might be necessary to minimize the geometrical miss and deliver the planned doses to the target tissue and normal structure provide best results with minimum toxicity by maintaining a bladder volume of about 100 mL and an empty rectum during the whole course of treatment. The daily anatomical shift and contour of the patients maintaining a bladder volume of approximately 100 mL with an empty rectum may result in asymmetrical conforming to the planning target volume and hence appropriate and adequate planning target volume margins are required