3D printer-based novel intensity-modulated vaginal brachytherapy applicator: feasibility study

Abstract

Purpose: To design a novel high-dose-rate intracavitary applicator which may lead to enhanced dose modulation in the brachytherapy of gynecological cancers. Material and methods: A novel brachytherapy applicator, auxiliary equipment and quality control phantom were modeled in SketchUp Pro 2017 modeling software and printed out from a MakerBot Replicator Z18 three-dimensional printer. As a printing material polylactic acid (PLA) filament was used and compensator materials including aluminum, stainless-steel and Cerrobend alloy were selected according to their radiation attenuation properties. To evaluate the feasibility of the novel applicator, two sets of measurements were performed in a Varian GammaMed iX Plus highdose rate iridium-192 (192 Ir) brachytherapy unit and all of the treatment plans were calculated in Varian BrachyVision treatment planning system v.8.9 with TG43-based formalism. In the first step, catheter and source-dwell positioning accuracy, reproducibility of catheter and source positions, linearity of relative dose with changing dwell times and compensator materials were tested to evaluate the mechanical stability of the designed applicator. In the second step, to validate the dosimetric accuracy of the novel applicator measured point dose and two-dimensional dose distributions in homogeneous medium were compared with calculated data in the treatment planning system using PTW VeriSoft v.5.1 software. Results: In mechanical quality control tests source-dwell positioning accuracy and linearity of the designed applicator were measured as ≤ 0.5 mm and ≤ 1.5%, respectively. Reproducibility of the treatment planning was ≥ 97.7% for gamma evaluation criteria of 1 mm distance to agreement and 1% dose difference of local dose. In dosimetric quality control tests, maximum difference between measured and calculated point dose was found as 3.8% in homogeneous medium. In two-dimensional analysis, the number of passing points was greater than 90% for all measurements using gamma evaluation criteria of 3 mm distance to agreement and 3% dose difference of local dose. Conclusions: The novel brachytherapy applicator met the necessary requirements in quality control tests.

Design and evaluation of 3D printable patient‐specific applicators for gynecologic HDR brachytherapy

“…The stainless steel-based materials have intermediate stopping power and potentially might be used in regions, requiring partial coverage, not investigated here. 4 This investigation has also presented a versatile raytracing algorithm allowing definition of the shielded/unshielded regions of the applicator, taking into account the patient-specific geometry of the target volume and OARs and planned dwell positions of the source. While this was tested on the example of a single-channel applicator geometry presented in TG-186 report, the algorithm can be easily modified to accommodate multichannel applicators for optimal target coverage.…”

“…We note that previous studies describing 3D printable shielded gynecological applicators included shielding only in the cylindrical part of the applicator leading to inevitable exposure of external os of the cervix. 4,5 In this study, the suggested algorithm calculates shielding throughout the entire applicator geometry and allows for dose modulation through the top semi-spherical dome of the applicator (see Figs. 4,6,7), which might be advantageous for patient outcomes.…”

“…2,3 In such conditions, the target volume is frequently localized to an area 5 mm deep within the vaginal wall, which can be adequately accessed with a cylindrical applicator. 4,5 Use of three-dimensional (3D) printing technology for HDR BT applicator manufacturing has shown advantages through customization of applicator size, shape, and internal structure according to the needs of each patient. [6][7][8][9] Dose uncertainty and patient discomfort might be reduced by manufacturing a custom applicator, which is best suited to individual patient anatomy.…”

“…Furthermore, the target coverage can be significantly improved by accommodating the patienttailored channels for interstitial catheters to the applicator design. 4,6,8,[10][11][12][13][14] Today, a range of biocompatible and sterilizable 3D printable materials is available, each with different radiologic properties. They are composed of biocompatible polycarbonate/polypropylene resin, while some also contain inclusion of heavy metals, which paves the way for 3D dose modulation within the patient.…”

“…In previous investigations, this shielding has been 3D printed or machined in the shape of 45 or 90 degree wedges and provides continuous attenuation along their entire length. 4,15,16 Skinner et al have suggested a circular shielding design, that provides dose modulation along the length of the shield, based on a 2D dose calculation algorithm. 5 This approach is simplistic, given that the total dose at any point around the applicator is composed of dose contributions from the multiple source dwell positions.…”