A novel use of 3D-printed template in vaginal HDR brachytherapy

The High-Dose-Rate (HDR) vaginal cylinder treatment is typically designed using the initial CT, while the subsequent implants are verified using rudimentary methods (i.e., visual inspection, ruler measurements, etc.) and/or X-ray imaging. We are proposing the use of a 3D-printed individualized template that could provide simple and reproducible vaginal cylinder insertion.

Six patients were included in the study with prescriptions of 6 Gy/fraction for 2 to 5 fractions (total 27 treatments). The first 1 to 2 treatments were delivered without the template and the rest with the CT-based 3D-printed templates. Cone beam CTs (CBCTs) were acquired to verify the cylinder placement for all treatments. D_2cc of the bladder and rectum are recorded on both planning CT and the following on-treatment CBCTs.

By using the templates, the tip position variation on average (±1 SD) reduced from 0.8±0.5 cm to 0.6±0.4 cm, and angular difference decreased from 5.3±3.5° to 4.7±2.4°. The pitch and yaw deviation are reduced from 0.9 ± 5.8° and 0.4±2.9° to 0.0±3.9° and -0.2±3.0°, respectively. The deviation of D_2cc to bladder from the plan reduced from 6±4% to 5±3%, and rectum from 5±2% to 4±4%.

The 3D-printed patient-specific cylinder templates could potentially improve the geometrical reproducibility of cylinder treatments at no cost of additional imaging. The D_2cc for the bladder and rectum are determined by the treatment length rather than their respective volumes.