CT-guided high–dose-rate dose prescription for cervical carcinoma: the importance of uterine wall thickness•

Purpose: To evaluate the use of CT imaging to guide dose prescription for high-dose-rate brachytherapy in cervical cancer, by defining the uterine wall thickness and the proximity of the rectosigmoid, bladder, and small bowel. Methods and Materials: From 1994–2000, 40 patients with cervical cancer underwent treatment with external beam radiation therapy plus high–dose-rate brachytherapy. A pelvic CT scan was performed following applicator placement, and was analyzed to determine anterior and posterior uterine wall thickness, and the distance to the bladder and rectosigmoid. The dose prescription was initially at Point A, but in some patients, was altered based on the thickness of the uterine wall. Results: Measurements in the region of the lower and upper uterine wall were analyzed separately. Nearly half (46%) of the patients had an average anterior or posterior wall thickness of <20 mm. A correlation was observed between thinner anterior lower uterine walls and increased late bladder and ureteral toxicity, and between thinner anterior upper uterine walls and increased late small-bowel toxicity. Conclusions: A significant number of patients have uterine walls <2 cm in thickness. The use of CT imaging can identify patients in whom the conventional dose specification point may need to be altered to maintain the therapeutic ratio.