A novel 3D-printed brachytherapy applicator and monte Carlo model for the treatment of conjunctival tumors.

To develop a custom low dose rate brachytherapy applicator for the treatment of conjunctival malignancies which leverages 3D-printing technology to provide enhanced design flexibility and availability. An elliptical shell applicator inspired by ocular surgery postoperation conformer shells was developed for the placement of the applicator around the cornea of the eye, with a central hole to provide patient comfort. The applicator featured 2 concentric circles of slots for iodine-125 seeds, providing customization of the dose distribution depending on the location of the target. The applicator was modeled using computer-aided design software. The resultant model STL file was used for 3D printing of the applicator and the development of a Monte Carlo model of the applicator and its dose distribution. The applicator was successfully 3D printed using biocompatible resin, which could be sterilized for treatment after manual source loading. A Geant4 model of the applicator was created directly from the STL model and was applied to a phantom to estimate the dose distribution delivered by the applicator. The toroidal dose distribution allowed for treatment of the conjunctiva while reducing dose to the cornea compared to traditional eye plaque designs. A custom 3D-printed applicator was successfully developed and modeled for the treatment of conjunctival malignancies. This novel applicator design potentially provides higher quality, more customizable dose distributions for patients and the simplicity of the design makes it accessible for any clinic with 3D-printing technology.

Matrosic CK ，Kronenberg S ，Demirci H ，Hayman JA ，Han H ，Lee C ... -  《-》

Measured, calculated, and egs_brachy I-125 dose distributions in a gold plaque for retinoblastoma treatment.

This study measured and calculated dose distributions around a unique gold plaque for whole-eye radiotherapy (to treat retinoblastoma). The applicator consists of a pericorneal ring attached to the four extraocular muscles and four legs, each loaded with I-125 seeds. They are inserted beneath the conjunctiva in-between each pair of muscles and attached anteriorly to the ring. The applicator was designed in such a way that the dose is directed toward the middle of the eye while sparing surrounding tissues. (I) To compare the measured and calculated data obtained by thermoluminescent dosimeters (TLDs) in a solid-water phantom, a Gafchromic film in a solid-water phantom, the treatment planning systems, and Monte Carlo simulations; (II) to use Monte Carlo simulations for the determination of the dose to the organs at risk by taking the gold shielding and the anisotropy into account. The dose around the applicator was measured using TLDs and Gafchromic EBT2 film in eye-shaped solid-water phantoms. Dose calculations were performed with the TheraPlan Plus and BrachyVision planning system and Monte Carlo simulations with egs_brachy code. A computer-aided design drawing of the applicator was created and used to create the input file for the Monte Carlo simulations. Monte Carlo calculated dose to the optic nerve is 64.8% of the central dose in the eye, whereas the planned dose is 93.7%. The Monte Carlo lens dose varies from 72.0% to 86.1%, whereas the planned dose varies from 73.0% to 84.3%. Monte Carlo-calculated dose to the bony orbit is 11.3%, whereas the planned dose is as high as 54.7% compared to the dose in the center region of the eye. The measured and Monte Carlo-simulated dose distributions matched well, whereas planned dose distributions showed discrepancies in some areas of the eye and outside of the eye due to their ignorance of the shielding effects of the plaque.

Trauernicht CJ ，van Eeden D ，du Plessis FCP 《-》

A generic TG-186 shielded applicator for commissioning model-based dose calculation algorithms for high-dose-rate (192) Ir brachytherapy.

A joint working group was created by the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) with the charge, among others, to develop a set of well-defined test case plans and perform calculations and comparisons with model-based dose calculation algorithms (MBDCAs). Its main goal is to facilitate a smooth transition from the AAPM Task Group No. 43 (TG-43) dose calculation formalism, widely being used in clinical practice for brachytherapy, to the one proposed by Task Group No. 186 (TG-186) for MBDCAs. To do so, in this work a hypothetical, generic high-dose rate (HDR) 192 Ir shielded applicator has been designed and benchmarked. A generic HDR 192 Ir shielded applicator was designed based on three commercially available gynecological applicators as well as a virtual cubic water phantom that can be imported into any DICOM-RT compatible treatment planning system (TPS). The absorbed dose distribution around the applicator with the TG-186 192 Ir source located at one dwell position at its center was computed using two commercial TPSs incorporating MBDCAs (Oncentra® Brachy with Advanced Collapsed-cone Engine, ACE™, and BrachyVision ACUROS™) and state-of-the-art Monte Carlo (MC) codes, including ALGEBRA, BrachyDose, egs_brachy, Geant4, MCNP6, and Penelope2008. TPS-based volumetric dose distributions for the previously reported "source centered in water" and "source displaced" test cases, and the new "source centered in applicator" test case, were analyzed here using the MCNP6 dose distribution as a reference. Volumetric dose comparisons of TPS results against results for the other MC codes were also performed. Distributions of local and global dose difference ratios are reported. The local dose differences among MC codes are comparable to the statistical uncertainties of the reference datasets for the "source centered in water" and "source displaced" test cases and for the clinically relevant part of the unshielded volume in the "source centered in applicator" case. Larger local differences appear in the shielded volume or at large distances. Considering clinically relevant regions, global dose differences are smaller than the local ones. The most disadvantageous case for the MBDCAs is the one including the shielded applicator. In this case, ACUROS agrees with MC within [-4.2%, +4.2%] for the majority of voxels (95%) while presenting dose differences within [-0.12%, +0.12%] of the dose at a clinically relevant reference point. For ACE, 95% of the total volume presents differences with respect to MC in the range [-1.7%, +0.4%] of the dose at the reference point. The combination of the generic source and generic shielded applicator, together with the previously developed test cases and reference datasets (available in the Brachytherapy Source Registry), lay a solid foundation in supporting uniform commissioning procedures and direct comparisons among treatment planning systems for HDR 192 Ir brachytherapy.

Ma Y ，Vijande J ，Ballester F ，Tedgren ÅC ，Granero D ，Haworth A ，Mourtada F ，Fonseca GP ，Zourari K ，Papagiannis P ，Rivard MJ ，Siebert FA ，Sloboda RS ，Smith R ，Chamberland MJP ，Thomson RM ，Verhaegen F ，Beaulieu L ... -  《-》

Reproducibility and air gap pockets of 3D-printed brachytherapy applicator placement in high-dose-rate skin cancer.

This study aimed to investigate the reproducibility of a novel approach using 3D printed brachytherapy applicators for the treatment of skin cancer. Specifically, we aimed to assess the accuracy of applicator placement and to minimize the existence of air gap pockets between the applicator and the patient's skin. A total of 20 patients plans diagnosed with skin cancer were enrolled in this study. All patients underwent high dose rate (HDR) brachytherapy. To ensure precise applicator placement, patient-specific 3D printed applicators were designed based on individual body and tumor topography, utilizing data obtained from computer tomography (CT) scans. All applicators were fabricated using fused deposition modeling technology. The error in applicator placement was measured and found to be less than 1.0 mm on average, with a standard deviation of 0.9 mm. Additionally, the average error in air gap pockets between the applicator and the patient's skin was 0.4 mm (standard deviation was 0.5 mm). The study demonstrated that the personalized approach of 3D printed brachytherapy applicator placement in skin cancer treatment yielded highly accurate results. The average error of less than 1.0 mm in applicator positioning and the minimal air gap pockets demonstrated the reproducibility and precision of this technique. Our study establishes the reproducibility and accuracy of 3D-printed brachytherapy applicator placement in the treatment of skin cancer. This personalized treatment approach offers a highly precise method for delivering radiation therapy, minimizing the risk to adjacent healthy tissues, and enhancing overall patient outcomes.

Poltorak M ，Banatkiewicz P ，Poltorak L ，Sobolewski P ，Zimon D ，Szwast M ，Walecka I ... -  《-》

Intensity modulated Ir-192 brachytherapy using high-Z 3D printed applicators.

Skinner LB ，Niedermayr T ，Prionas N ，Perl J ，Fahimian B ，Kidd EA ... -  《-》