The fats, cavities, organ) to print with 3D

The function of phantom has equipment
calibration, quality assurance, dose verification and teaching, surgical guidance 1-4. Phantom scanning and testing
can repeat the shooting conditions infinitely. To accurately simulate a real
patient scan, the model should be as close as possible to the patient’s shape
and attenuation characteristics 5. Phantom’s geometry should be represent the
patient’s shape and physique.3D printed phantom can do this, but most of the 3D
printers that product phantom are photo-curing. The high material costs and the
limitations of the printed material can’t be popularized to personal
laboratories 6.

Therefore, we proposed the idea of
using 3D printing to meet individual needs and fill the equivalent material to
satisfy the attenuation characteristics 7. We experimented with a variety of
materials to select the relatively eligible agarose, M3 waxes, CaCO3
and MgO. After pre-experiments, we got the right ratio to simulate fat and
muscle. We found that Fabian Adams and us have similar ideas, their kidney
phantom also chose agarose 8. The purpose of our study was to create
anthropomorphic phantoms for individual patients with human anatomy and
radiation attenuation properties.

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Bone tissue can use equivalent
materials for 3D printing directly. However, because of the limitations of 3D
printed materials, it is not desirable for other tissues (muscles, fats,
cavities, organ) to print with 3D printed materials, so we used a method of
printing the outer shell first and then filling the equivalent material inward.

2.
Materials and Methods:

2.1 Three-dimensional
design

Using a Brilliance ? ICT scanner
(Philips, Netherlands), patient was scanned to obtain two CT data samples
(Department of Radiation Oncology, Cancer Hospital of Hubei Province). Scanning
range: chest. Scanning conditions: tube voltage 120kV, current 260mA, layer
thickness 0.5mm, scanning layer 596 layers, axial scanning. The obtained DICOM
images were imported into Mimics Research 17.0 image analysis software
(Materialize, Belgium). The chest mold is divided into ribs, scapula, sternal
angle, fat tissue, muscle tissue, lung tissue, diseased tissue. Based on the
patient’s CT image data, each part of the skeleton and tissue were divided and
reconstructed three-dimensionally.

And then different tissues were
stained and modeled using the threshold method. The finished model is
shell-processed: first, the model is thickened, and then subtracted the
original model to obtain a shell. Using the Magic10.0 software (Materialize,
Belgium), the models were derived by lubrication and noise elimination.

Thoracic models are required to obtain
3D of fat tissue, lung tissue, ribs, scapula, and sternal angle, as shown in
Figure 1. The outer shell of the 3D model of fat tissue and lung tissue is
obtained. Shell thickness is set to 2.5mm. The three-dimensional mode of fat
tissue shell, lung tissue shell, ribs, scapula, sternal was transformed by
Magic10.0 software to achieve solid generation and noise reduction. Then export
all three-dimensional model, shown in Figure 2.

 

2.2. Printing 3D models and printed
materials

Import 3D
models in STL format to 3D printer for printing. The casing is printed with
regular print material and the bone tissue is printed with equivalent material.

The fat tissue
shell in the chest mold, the lung tissue shell is printed with ABS plastic (conventional
printing material). Ribs, sternum angle, scapula use modified epoxy resin
emulsion polymer resin active material as bone tissue radiation equivalent
material 9, shown in Figure3 and Figure4.

 

2.3. Selection of radiation
equivalent materials for the organization

Different tissues of human body are different in CT
value. Equivalent materials of each organization were pre-tested by radiation
equivalent material and selected by CT equivalent test 10. After several
experiments of material proportion, the equivalent material proportion of each
tissue was determined. A variety of equivalent materials, can meet the high
plasticity, high stability, high security, high degree of uniformity based on
the choice 11.

The following is the selection of chest
tissue material, ratio and production process.

?Fat tissue: The melted M3 wax was selected as the solvent, CaCO3
(1%) and MgO (12%) were used as solutes. The M3 wax was kept at a melting point
of 124 degrees Fahrenheit in a water bath, and MgO and CaCO3 were
added thereto. After sufficiently stirring, the wax was filled into the fat
area and allowed to cool and solidify.

? Muscle tissue: Water was selected as a solvent, with 2%
agarose, 1% NaCl, 0.8% pearl powder as solute. Agarose is first added to the
water, heated at high temperature and stirred constantly to form a suspension,
and then added pearl powder, NaCl, and then heated, stirred, when it reaches a
transparent state, cooled and stirred at 120 degrees Fahrenheit, State, when
the temperature reaches 130 degrees Fahrenheit, filling to the muscle tissue,
cooling and solidification.

? Focal tissue: Consistent with the method of making muscle
tissue, but the ratio is different, the lesion selected water as solvent, with
2.5% agarose, 1% NaCl, 1% pearl powder as solute.

? Lung tissue?The foamed silica gel is made up of silica gel and curing agent
by 1:1. The silica gel was injected directly into the outer layer of the lung
tissue.

3. Results

Projects
using 3D printing phantom involve 3D design, 3D printing and post-processing.
The use of assembly design in 3D designs increases the flexibility of each part
and adds special design. The use of equivalent materials in post-processing
also gives great flexibility, for example chemical materials, animal tissues
and cultured human tissues can be used instead of solutions.

Adding additives to the material to
ensure the accuracy of the CT value, the improved material can more accurately
simulate the organization. Comparison of unmodified and
improved materials?shown
in Figure 4 and Table 2. The phantom was shown in Figure 5.

 

CT
imaging of the chest mold, the resulting image is highly similar to the real
human CT image morphology, shown in Figure 6?Figure 7. The CT value of each part
was extracted from each CT image, and the CT value range of each part was
obtained. The range of the CT value deviation of each part is very small, as
shown in Table 1, which can fully reflect the differences among different
organizations.

4. Discussion

Three-dimensional?3D?printing technology is
adopted to make the production method simple and fast. The
ordinary 3D printers will be able to meet the 3D printing conditions, and
accurate personalized design can reflect the individual physiological and
pathological features. This method can simulate more CT values.  In addition to the already enumerated chest
phantom, more complex phantoms can be created, such as pelvis, cranial head and
other complicated parts. The procedure is consistent with that of the ontology.
We can choose different equivalent materials according to different CT
values.

In summary, in this study, because of
the precision of 3D printing technology and the fact that the phantom shape is
truly human, the accuracy and individuation
of the phantom meet the clinical requirements and quality control standards.
The phantom can serve as a surrogate for the human body in diagnosis,
treatment, teaching, and radiation standard studies, as well as for dose
visualization .

Ehler 12 used fused deposition
printing technology to make anthropomorphic phantoms for dose measurement of
radiation therapy. Mayer 13 presented a chest model of radiation therapy
using a PolyJet printer. G Menikou 14used a 3D printed MRI compatible head
phantom to evaluate the ultrasound solution. F Adams’s soft phantoms were
constructed using a novel technique that combines 3D wax printing and polymer
molding 15.R Rai?J Ceh and J Jung Research on Bone
and Lung Tissues Using 3D Printing Techniques, D Mitsouras for MRI, ST Bache
for Small Animal Experiments, and 3D Printing for Phantom Applications 16-20.Despite
the advanced technology, these methods are still complicated. In
addition, due to the simplicity of the material
produced, it can’t
reach the level of simulating real human body. The various materials we added
in the experiment to ensure that the body’s radiation attenuation properties.

The method of this paper also has some
shortcomings. 3D printer specifications will restrict the size of the print
casing, making it very difficult to make full-body phantom with the split print
stitching. We need to accurately know the dissolution of the materials, because
if the solution concentration is not uniform, the effect will be very poor.
Smaller casing settings provide good imaging, but also more fragile, so it is
necessary to accurately estimate thickness based on site and method of
manufacture. Although the production of such phantom is simple and convenient,
it still needs further exploration and improvement for large-scale clinical
applications.

For materials, we choose the
equivalent material, because of its adjustable ct value, can be widely used in
the production of various human body phantom organizations, such as the liver,
kidney and other parenchymal organs, can meet the organizational equivalent.
Because of the simplicity of 3D printing phantoms, laboratory production is
achieved, requiring complex industrial customization without the need for
traditional phantom fabrication methods. As printing materials continue to
evolve, it is even possible to print out the equivalent materials for each
organization instead of using filling.

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