Assessment of Applicator Stability In Gynecological Brachytherapy
Abstract
Purpose
To evaluate the stability of interstitial applicators, secured using a belt-and-ties system, during gynecological high-dose rate brachytherapy (HDRBT) delivered over 3 days using a single implant.
Methods
Dwell positions were digitized on CT images from 34 patients treated between 2020 and 2025. Each patient had a planning CT scan acquired immediately post-insertion and a second CT taken on day 2 of treatment to verify applicator positioning. The two scans were registered by a clinical medical physicist. Applicators used included commercially available intracavitary cylinders paired with interstitial perineal template needles (n=11); and in-house 3D-printed patient-specific cylindrical templates (PSCTs) (n=23), some of which were also paired with perineal templates (n=6). All applicators were secured using sets of 4 cloth ties attached to a belt placed about the patient’s waist. Applicator stability was evaluated by calculating dwell position displacements (absolute, S-I, A-P, and R-L) between scans.
Results
The median absolute displacement of all dwell positions was 1.5 mm (IQR 0.8, 2.2). The median absolute displacement of dwell positions of catheters in PSCTs was 1.3 mm (IQR 0.8, 2.0); in commercially available cylinders was 1.8 mm (IQR 1.0, 3.2); and in perineal template needles was 1.7 mm (IQR 1.0, 2.7). The median displacement of all dwell positions in the superior direction was -0.1 mm (IQR -1.0, 0.8); in the posterior direction was -0.1 mm (IQR -0.6, 0.3); and in the left direction was 0.0 mm (-0.3, 0.3).
Conclusion
Regardless of the applicator type, the belt-and-ties method of securing the applicators resulted in stable implants, with motion uncertainties on the order of 2 mm. PSCTs showed smaller inter-fraction position changes compared to commercially available intracavitary cylinders and perineal templates, though the differences were not statistically significant. Future analysis will evaluate the effect of displacement on dosimetry.