HDR Applicator for Improved Dosimetry to Vaginal Cuff “Dog Ears”
Abstract
Purpose
To improve prescription dose coverage while limiting surface dose of vaginal cuff “dog ears” during a high dose rate brachytherapy treatment by creating a universally usable applicator that allows for lateral expansion.
Methods
Using Autodesk Fusion CAD software and a Prusa 3D printer with PLA filament, a prototype for the applicator was developed. The applicator has 9 channels and allows for a 5-degree expansion of the lateral segments, allowing for variable change of the lateral diameter at the tip between 30 mm to ~60 mm. The applicator was then CT scanned in air in a closed position, a symmetrically opened position, and an asymmetrically opened position, and hypothetical targets were created for each scenario. Elekta Oncentra’s inverse planning by simulated annealing (IPSA) algorithm was used to optimize the dose distribution in each scenario, simulating a single channel cylinder (SCC) compared to the prototype applicator.
Results
Dose volume histogram analysis showed the prototype applicator improved prescription coverage of the target by 8.9% in the asymmetrical scenario and by 5.6% in the symmetrical scenario. Using a 2mm expansion around the applicator to represent surface dose, the V200% at the surface was reduced by 53.8% in the asymmetric case and by 60.6% in the symmetrical case, though the prototype applicator did demonstrate greater D.01cc in both scenarios due to its multi-channel nature.
Conclusion
Initial testing of the prototype applicator demonstrates improved dosimetry over a SCC in these limited, idealized scenarios. Next steps are to create a more robust test of the applicator’s capabilities by creating a medical-grade prototype for potential use in in-vivo studies. The long-term goal would be to improve the standard of care for patients and further reduce the probability of recurrence for patients with the “dog ear” feature without increasing the risk of acute toxicities.