Cone Beam CT-Based Three-Dimensional Planning in High-Dose-Rate Brachytherapy for Cervical Cancer

Purpose: To evaluate dose-volume histograms (DVHs) of bladder and rectum from the use of cone beam CT (CBCT)-based three-dimensional (3D) treatment planning in intracavitary high-dose-rate brachytherapy (HDRB) for cervical cancer patients and to compare these parameters with International Commission on Radiation Units and Measurements (ICRU) of rectal and bladder reference point dose measurements. Methods and Materials: Thirteen patients with cervical cancer underwent HDRB insertions. CT-compatible tandem and ovoid applicators were used to obtain intraoperative CBCT images. The use of a rectal tube and injection of bladder contrast before scanning facilitated contouring the rectum and bladder. All patients underwent intraoperative orthogonal x-ray filming, and treatments were prescribed using standard two-dimensional planning and dosimetry. DVHs for the bladder and rectum were constructed for each treatment. The minimum dose in the most irradiated 2.0-cm³ volume of bladder (B_D2V) and rectum (R_D2V) were determined from DVHs and compared to ICRU reference point estimates of bladder (B_ICRU) and rectum (R_ICRU) doses. Results: Twenty-six CBCT-based plans were evaluated. The median B_ICRU dose (347 cGy; range, 164-601 cGy) was significantly lower (p < 0.001) than the median B_D2V (594 cGy; range, 260-969 cGy). The median R_ICRU dose (405 cGy; range, 189-700 cGy) was also significantly lower (p = 0.037) than the median R_D2V (488 cGy; range, 227-786 cGy). Conclusions: CBCT-based 3D planning can be used in HDRB for cervical cancer and is a convenient alternative to CT-based planning, with the advantage of minimizing applicator motion. Correlation with late effects will further define the role of CBCT-based 3D dosimetry in HDRB planning.