On the gamma radiation response of commercially available 3D printing materials for medical dosimetry.

3D printing technology has rapidly spread for decades, allowing the fabrication of medical implants and human phantoms and revolutionizing healthcare. The objective of this study is to evaluate some radiological properties of commercially available 3D printing materials as potential tissue mimicking materials. Among fifteen materials, we compared their properties with nine human tissues. In all materials and tissues, exposure and energy absorption buildup factors were calculated for photon energies between 0.015 and 15 MeV and penetration depths up to 40 mean free path. Furthermore, the Geant4 Monte Carlo toolkit (version 10.5) was used to simulate their percentage depth dose distributions. In addition, equivalent atomic numbers, effective atomic numbers, attenuation coefficients, and CT numbers have been examined. All parameters were considered in calculating the average relative error (σ), which was used as a statistical comparison tool. With σ between 6 and 7, we found that Polylactic Acid (PLA) was capable of simulating eye lenses, blood, soft tissue, lung, muscle, and brain tissues. Moreover, Polymethacrylic Acid (PMAA) material has a σ value of 4 when modeling adipose and breast tissues, respectively. Aside from that, variations in 3D printing materials' infilling percentage can affect their CT numbers. We therefore suggest the PLA for mimicking soft tissue, muscle, brain, eye lens, lung and blood tissues, with an infill of between 92.7 and 94.3 percent. We also suggest an 89 percent infill when simulating breast tissue. Furthermore, with a 96.7 percent infill, the PMAA faithfully replicates adipose tissue. Additionally, we found that a 59 percent infill of Fe-PLA material is comparable to cortical bone. Due to the benefits of creating individualized medical phantoms and equipment, the results might be seen as an added value for both patients and clinicians.

Monte Carlo study of patient and medical staff radiation exposures during interventional cardiology.

The aim of this study is to assess the radiation exposure of the patient and the medical staff during interventional cardiology procedures. Realistic exposure scenarios were developed using the adult reference anthropomorphic phantoms adopted by the International Commission on Radiological Protection (ICRP110Male and ICRP110Female), and the radiation transport code Geant4 (version 10.3). The calculated equivalent and effective doses were normalised by the simulated Kerma-Area Product (KAP), resulting in two conversion coefficients HT/KAP and E/KAP. To properly evaluate the risk of exposure, several dose-dependent parameters have been investigated, namely: radiological parameters (tube kilovoltage peak (kVp), type of projection, field size (FOV)), and operator positions. Four projections (AP,PA,LAO25° and RAO25°) were simulated for three X-ray energy spectra (80,100 and 120 kVp) with four different values of FOV (15×15 cm2,20×20 cm2,25×25 cm2 and 30×30 cm2). The results showed that the conversion coefficients values increase with increasing tube voltage as well as the FOV size. Recommended projection during the interventional cardiology procedures, whenever possible, should be the PA projection rather than AP projection. The most critical projection for the patient and the main operator is the RAO25° projection and the LAO25° projection respectively. The comparison of our results with the literature data showed good agreement allowing their use in the dosimetric characterization of interventional cardiology procedures.

NEURAL NETWORK MODELLING OF CARDIAC DOSE CONVERSION COEFFICIENT FOR ARBITRARY X-RAY SPECTRA.

In this article, an approach to compute the dose conversion coefficients (DCCs) is described for the computational voxel phantom 'High-Definition Reference Korean-Man' (HDRK-Man) using artificial neural networks (ANN). For this purpose, the voxel phantom was implemented into the Monte Carlo (MC) transport toolkit GEANT4, and the DCCs for more than 30 tissues and organs, due to a broad parallel beam of monoenergetic photons with energy ranging from 15 to 150 keV by a step of 5 keV, were calculated. To study the influence of patient size on DCC values, DCC calculation was performed, for a representative body size population, using five different sizes covering the range of 80-120 % magnification of the original HDRK-Man. The focus of the present study was on the computation of DCC for the human heart. ANN calculation and MC simulation results were compared, and good agreement was observed showing that ANNs can be used as an efficient tool for modelling DCCs for the computational voxel phantom. ANN approach appears to be a significant advance over the time-consuming MC methods for DCC calculation.

MONTE CARLO STUDY OF THE CARDIAC ABSORBED DOSE DURING X-RAY EXAMINATION OF AN ADULT PATIENT.

The computational voxel phantom 'High-Definition Reference Korean-Man (HDRK-Man)' was implemented into the Monte Carlo transport toolkit Geant4. The voxel model, adjusted to the Reference Korean Man, is 171 cm in height and 68 kg in weight and composed of ∼30 million voxels whose size is 1.981 × 1.981 × 2.0854 mm3 The Geant4 code is then utilised to compute the dose conversion coefficients (DCCs) expressed in absorbed dose per air kerma free in air for >30 tissues and organs, including almost all organs required in the new recommendation of the ICRP 103, due to a broad parallel beam of monoenergetic photons impinging in antero-postero direction with energy ranging from 10 to 150 keV. The computed DCCs of different organs are found to be in good agreement with data published using other simulation codes. Also, the influence of patient size on DCC values was investigated for a representative body size of the adult Korean patient population. The study was performed using five different sizes covering the range of 0.8-1.2 magnification order of the original HDRK-Man. It focussed on the computation of DCC for the human heart. Moreover, the provided DCCs were used to present an analytical parameterisation for the calculation of the cardiac absorbed dose for any arbitrary X-ray spectrum and for those patient sizes. Thus, the present work can be considered as an enhancement of the continuous studies performed by medical physicist as part of quality control tests and radiation protection dosimetry.

Monte Carlo studies of the Tunisian gamma irradiation facility using GEANT4 code.

This paper describes a complete Monte Carlo study of the Tunisian gamma irradiation facility (CNSTN) using the GEANT4 CERN's code. The work focused on the optimization of the absorbed dose distribution inside the irradiation cell, with and without product. For this purpose, 32 different points at the middle plane of the source rack, 29 positions along Z axis and 7 critical points, were carried out using PMMA dosimeters. Then, to achieve a given bulk density, boxes loaded with "dummy" product were used. Simulated and experimental results are compared and good agreement is observed. It is shown that Monte Carlo simulation improves process understanding, predicts absorbed dose distributions and calculates dose uniformity within product.

Effects of mitomycin C on glaucoma filtration capsules.

One of the leading causes of implantable device failure is build up of scar tissue on the device. Approaches to address this complication range from choosing device materials that prevent cell adhesion to treatment with potent antifibrotic medications such as mitomycin C. We examined the collagen matrix around aqueous shunt implants in rabbit eyes and found the filtration capsule formed around these devices is not composed of scar tissue. Rather collagen deposition is highly organized with collagen bundles oriented along stress axes. We also examined adjacent tissue deposition in mitomycin C treated animals and found decreased vascularization, condensed collagen in Tenon's capsule with more collagen bundles less well formed than those in the control eye of the same animal. The sclera was thicker under the plate than at the opposite side of the same eye. Structural and functional evaluation correlates with the clinical paradox that patients treated with mitomycin C have lower initial pressures with adjunct drug treatment but lower success rates than the control population after 18 months.

Surface tension controls capsule thickness and collagen orientation in glaucoma shunt devices.

Surgical implants to shunt aqueous humor from the eyes of glaucoma patients have been used with limited success, due to a buildup of fibrous tissue in the capsule that causes it to fail as a filtration device. Previous studies suggested that fibers orient along the principal stress lines--surface tension on the capsule directs collagen growth in order to strengthen the stretched membrane. The more tension on the capsule, the thicker the fibrous matrix. In the present study, we analyze collagen fibril and fiber bundle structure to determine whether similar stresses were placed on capsules formed around different implants. We used transmission electron micrographs and light microscopy. Results showed similar structure and collagen fiber bundle densities. This confirmed our previous conclusion that choosing a geometry that reduces surface tension minimizes capsule fibrosis and improves filtration.