A Variably Shielded HDR Applicator: Design, Dosimetric Characterization, TPS Integration, and Proof-of-Concept
Abstract
Purpose
As HDR Brachytherapy has the potential to increase in popularity due to changes in reimbursement models, the potential of new treatment sites for the modality can be increased through increased oargan-at-risk sparing via integrated shielding. In this work, we present the design and characterization of an HDR applicator with modular shielding. Materials and
Methods
A 3cm dia. cylinder applicator is 3D printed as a proof-of-concept. Within this applicator are 6 triangular channels for the placement of tungsten rods. The tungsten shielding is designed to be removed during patient imaging and placed prior to treatment. The channels are offset from a central opening for the placement of an interstitial needle to act as source path. An Elekta micro-selectron afterloader and Ir-192 source are utilized to establish the angular attenuation patten on films placed at two depths. Additional measurements are collected via ionization chamber. Collected data is complied to create a TG-43 parameter set to commission a virtual source that models the custom shielding configuration of the applicator.
Results
The internal shielding is seen to attenuate between 3 HVL and 1 TVL for Ir-192. Shielding configurations studied included 50%, 66% and 83% shielding of the cylindrical angle. The dose was demonstrated to be able to be modeled in Varian’s BrachyVision TPS as well as within a simplified spreadsheet. Testing of the applicator within a mock clinical setting also demonstrated that the device was able to be imaged prior to the accurate and reproducible placement of shielding.
Conclusion
This work demonstrated the feasibility of HDR applicators to possess clinically viable internal shielding. Physicians have expressed interest in the potential of this applicator for use in the treatment of rectal carcinoma. Future Monte Carlo simulations and applicator modeling can hope to bridge the gap between the work established here and clinical implementation.