Session Item

To introduce and evaluate a new software for designing patient-specific 3D-printed combined intracavitary/interstitial (IC/IS) brachytherapy applicators by modifying build-up caps (sleeves) of the commercial CT/MR split-ring applicator (Eckert & Ziegler BEBIG).

A DICOM dataset was exported from Oncentra TPS (Elekta) containing CT images of the CT/MR split-ring applicator (5mm build-up cap), RT-structure set and RT-plan with 6 additional source-trajectories optimized in straight and oblique directions with respect to the applicator’s tandem. The dataset was imported into Adaptiiv's brachytherapy software (Adaptiiv Medical Technologies) where a CAD model of the widened sleeves were co-registered to the original 5mm sleeves. After co-registration was confirmed in all 2D viewing planes, all 6 source-trajectories were subtracted from the CAD model, forming needle tunnels with user-defined diameters. Using the same dataset, the trajectories were also subtracted into notches corresponding to the ‘‘Venezia’’ (Elekta) applicator system for needle guiding-tube fixation. The output of the software were two RT-structures and two STL files corresponding to the patient-specific design of the Montreal split-ring sleeves with subtracted needle tunnels and notches respectively. Spatial fidelity of the subtracted tunnels and notches were evaluated on RT-structures and on rendered STL files of the designed sleeves. Angles of the subtracted tunnels and notches were evaluated on the RT-structure of the designed applicator with respect to the reference geometry in the TPS. CloudCompare software was used to compare surface distances of the applicator RT-structure and its corresponding STL. Time was estimated as necessary to complete the software workflow.

Diameters and inter-trajectory distances (ITDs) of generated needle tunnels and notches were evaluated on the RT-structure of the designed applicator and found to be within ± 0.1mm with respect to the user input while diameters and ITDs of the needle tunnels and notches corresponding to the STL file were found to be ± 0.2 mm with respect to the user input. CloudCompare software demonstrated submillimeter agreement between surface distances of the DICOM-RT applicator structure and the corresponding STL file. The tunnel angles measured in sagittal and coronal planes on the RT structure of the designed applicator matched the source-trajectory angles created in the TPS within ± 0.2 degrees. The workflow in the Adaptiiv software took approximately 5 minutes to complete and did not require any specialized 3D-modelling skills. 

The novel technology and workflow presented provide a practical approach to efficient and accurate design of patient-specific needle tunnels for the novel 3D-printed Montreal split-ring applicator for adaptive IC/IS GYN brachytherapy.