Multi-jet fusion for additive manufacturing of radiotherapy immobilization devices: Effects of color, thickness, and orientation on surface dose and tensile strength.

Immobilization devices are used to obtain reproducible patient setup during radiotherapy treatment, improving accuracy, and reducing damage to surrounding healthy tissue. Additive manufacturing is emerging as a viable method for manufacturing and personalizing such devices. The goal of this study was to investigate the dosimetric and mechanical properties of a recent additive technology called multi-jet fusion (MJF) for radiotherapy applications, including the ability for this process to produce full color parts. Skin dose testing included 50 samples with dimensions 100 mm × 100 mm with five different thicknesses (1 mm, 2 mm, 3 mm, 4 mm, and 5 mm) and grouped into colored (cyan, magenta, yellow, and black (CMYK) additives) and non-colored (white) samples. Results using a 6 MV beam found that surface dose readings were predominantly independent of the colored additives. However, for an 18 MV beam, the additives affected the surface dose, with black recording significantly lower surface dose readings compare to other colors. The accompanying tensile testing of 175 samples designed to ASTM D638 type I standards found that the black agent resulted in the lowest ultimate tensile strength (UTS) for each thickness of 1-5 mm. It was also found that the print orientation had influence on the skin dose and mechanical properties of the samples. When all data were combined and analyzed using a multiple-criteria decision-making technique, magenta was found to offer the best balance between high UTS and low surface dose across different thicknesses and orientations, making it an optimal choice for immobilization devices. This is the first study to consider the use of color MJF for radiotherapy immobilization devices, and suggests that color additives can affect both dosimetry and mechanical performance. This is important as industrial additive technologies like MJF become increasingly adopted in the health and medical sectors.

Recent progress of 4D printing in cancer therapeutics studies.

Cancer is a critical cause of global human death. Not only are complex approaches to cancer prognosis, accurate diagnosis, and efficient therapeutics concerned, but post-treatments like postsurgical or chemotherapeutical effects are also followed up. The four-dimensional (4D) printing technique has gained attention for its potential applications in cancer therapeutics. It is the next generation of the three-dimensional (3D) printing technique, which facilitates the advanced fabrication of dynamic constructs like programmable shapes, controllable locomotion, and on-demand functions. As is well-known, it is still in the initial stage of cancer applications and requires the insight study of 4D printing. Herein, we present the first effort to report on 4D printing technology in cancer therapeutics. This review will illustrate the mechanisms used to induce the dynamic constructs of 4D printing in cancer management. The recent potential applications of 4D printing in cancer therapeutics will be further detailed, and future perspectives and conclusions will finally be proposed.

Modelling of mass transport and distribution of aptamer in blood-brain barrier for tumour therapy and cancer treatment.

The blood-brain barrier (BBB) is a strong barrier against the entrance of drugs, which has made brain cancer treatment a major challenge. We have previously shown that targeting transferrin receptors using aptamers increased brain drug delivery. To get a better understanding of this phenomenon, in the present article, a mathematical model based on the finite element method was developed accounting for the fluid flow and mass transport of the aptamer molecule inside an 8 µm capillary vessel across a 14 µm blood-brain barrier domain. The fluid flow and mass transport equations were coupled to calculate the blood velocity and aptamer concentration profiles across the BBB. It was identified that the thickness of the astrocyte and endothelial cell layers are key parameters affecting the concentration of the aptamer delivered to the last neuron dendrites in the BBB. The predicted efficacy of the drug delivery (Capt/Cin) of 10.9% to 13.8% was calculated at a porosity of 0.5 to 0.9, respectively, at a blood velocity of 0.38 mm/s, which was independent of the inlet concentration of the aptamer. This low efficacy was attributed to the mass transfer resistance across endothelial cells, astrocyte and pericyte layers, which decreased the concentration by 6.7%. It was also identified that the main mechanism of drug delivery is switched from convective mass transport in the capillary layer (with Peclet number > 50) to mixed convection mass transport (1 < Peclet number < 5) in the porous layers and to diffusion only once aptamer reached the brain parenchyma (Peclet number < 1).

Infill selection for 3D printed radiotherapy immobilisation devices.

3D printing provides new opportunities to create devices used during radiotherapy treatments, yet little is known about the effect process parameters play on the proposed devices. This study investigates the combined influence of infill pattern, infill density and print orientation on surface dose, as well as on the mechanical properties of 3D printed samples, identifying the optimal infill patterns for use in radiotherapy devices including immobilisation. Fused deposition modelling (FDM) was used to produce sixty samples in two orientations for surface dose measurement, utilising ten different infill patterns. Surface dose testing was performed using a Varian Trubeam linear accelerator with a 6 MV photon beam. A further one hundred and twenty tensile test samples, designed according to ASTM D638 type I standards, were evaluated using a 50 KN Instron 5969. On average, horizontally printed samples had a lower surface dose measurement compared to the vertically orientated samples, with the Stars infill pattern recording the lowest surface dose values in the horizontal orientation, while the Hilbert Curve recorded the lowest surface dose in the edge orientation. Tensile tests revealed the 3D Honeycomb infill pattern to have the highest ultimate tensile strength (UTS) in both horizontal and edge orientations. Overall, the Stars infill pattern exhibited the optimal balance of low surface dose and above average UTS. This study shows how infill patterns can significantly affect dosimetry and mechanical performance of 3D printed radiotherapy devices, and the data can be used by design engineers, clinicians and medical physicists to select the appropriate infill pattern, density and print orientation based on the functional requirements of a radiotherapy device.

A review of 3D printed patient specific immobilisation devices in radiotherapy.

BACKGROUND AND PURPOSE: Radiotherapy is one of the most effective cancer treatment techniques, however, delivering the optimal radiation dosage is challenging due to movements of the patient during treatment. Immobilisation devices are typically used to minimise motion. This paper reviews published research investigating the use of 3D printing (additive manufacturing) to produce patient-specific immobilisation devices, and compares these to traditional devices. MATERIALS AND METHODS: A systematic review was conducted across thirty-eight databases, with results limited to those published between January 2000 and January 2019. A total of eighteen papers suitably detailed the use of 3D printing to manufacture and test immobilisers, and were included in this review. This included ten journal papers, five posters, two conference papers and one thesis. RESULTS: 61% of relevant studies featured human subjects, 22% focussed on animal subjects, 11% used phantoms, and one study utilised experimental test methods. Advantages of 3D printed immobilisers reported in literature included improved patient experience and comfort over traditional methods, as well as high levels of accuracy between immobiliser and patient, repeatable setup, and similar beam attenuation properties to thermoformed immobilisers. Disadvantages included the slow 3D printing process and the potential for inaccuracies in the digitisation of patient geometry. CONCLUSION: It was found that a lack of technical knowledge, combined with disparate studies with small patient samples, required further research in order to validate claims supporting the benefits of 3D printing to improve patient comfort or treatment accuracy.