Dose comparison between prescription methods according to anatomical variations in intracavitary brachytherapy for cervical cancer

PURPOSE: We compared how doses delivered via two-dimensional (2D) intracavitary brachytherapy (ICBT) and three-dimensional (3D) ICBT varied anatomically. MATERIALS AND METHODS: A total of 50 patients who received 30 Gy of 3D ICBT after external radiotherapy (RT) were enrolled. We compared the doses of the actual 3D and 2D ICBT plans among patients grouped according to six anatomical variations: differences in a small-bowel V(2Gy), small bowel circumference, the direction of bladder distension, bladder volume, sigmoid V(3.5Gy), and sigmoid circumference. Seven dose parameters were measured in line with the EMBRACE recommendations. RESULTS: In terms of bladder volume, the bladder and small-bowel D(2cc) values were lower in the 150–250 mL bladder volume subgroup; and the rectum, sigmoid, and bladder D(2mL) values were all lower in the >250 mL subgroup, for 3D vs. 2D ICBT. In the sigmoid V(3.5Gy) >2 (mL) subgroup, the sigmoid and bladder D(2mL) values were significantly lower for 3D than 2D ICBT. The bladder D2mL value was also significantly lower for 3D ICBT, as reflected by the sigmoid circumference. In patients with a small bowel V(2.0Gy) >10 mL or small bowel circumference >15%, most dose parameters were significantly lower for 3D than 2D ICBT. The bladder distension direction did not significantly affect the doses. CONCLUSION: Compared to 2D ICBT, a greater bladder volume can reduce the internal 3D ICBT organ dose without affecting the target dose.