The relationship between the bladder and the cervix in patients undergoing intracavitary therapy

Previous studies have shown a poor correlation between bladder damage and bladder dosage in patients treated with radiation therapy, including intracavitary therapy for uterine tumours. This study was undertaken to investigate prospectively the relationship between the cervical os and the bladder in patients undergoing intracavitary treatment. The computed tomography scans of 59 patients undergoing intracavitary treatment were analysed. The upper limit of the undistended bladder relative to the os extended from 5.5 cm cephalic to the cervix to 4.0 cm below it. The distance from the central tube to the posterior bladder wall at the level of the cervix ranged from 1.5 cm to 4.2 cm. This was positively associated with size of ovoid (p = 0.022), though with considerable individual variation. A separate analysis failed to show a consistent correlation with age or stage of disease. Thirty-nine of the 59 patients (65.5%) had asymmetrical bladders. Of these, half had "slight" asymmetry and the others had "marked" asymmetry. The thickness of the vesico-vaginal septum varied from 0.5 cm to 2.9 cm but was difficult to assess in some patients. In patients treated with medium-sized ovoids and those with Stage IB and IIB disease, the distance to the bladder base is greatest, though there is marked individual variation. These investigations reveal a marked variation in bladder position relative to the cervix in patients undergoing intracavitary therapy. The position of the bladder cannot be accurately predicted by any of these clinical criteria and requires to be defined by a radiological technique in the individual patient.