Seoul: Assessing Infill Densities for Better 3D Printing of Models in Radiation Therapy

In the recently published ‘Radiological Characteristics of Materials Used in 3-Dimensional Printing with Various Infill Densities,’ researchers from the Veterans Health Service Medical Center in Seoul, Korea are assessing new materials for 3D printing.

With a focus on how infill densities affect 3D printing techniques, the research team considered a wide variety of materials, evaluated by examining their Hounsfield units—a measurement commonly used in the radiology field to measure radio density.

In this study, the researchers are even more specifically concerned with radiation oncology and the fabrication of improved compensators—tools that help target the exact areas where radiation is to be delivered to tumors. The key is to kill the tumor while preventing as much of the surrounding organs as possible from being exposed to radiation.

The technology of 3D printing offers great results in the medical field today by way of 3D printed medical models, devices like implants, prosthetics, and more, and a variety of guides. Here, metal compensators are fabricated after being completely customized to the patient’s shape, refining the uniformity of dosage—and offering an improvement over conventional methods.

3D printed models may also be used to target the radiation at the skin’s surface. The researchers point out that many efforts have been made so far to create better quality assurance in radiation therapy too by making phantoms, derived from CD data converted into 3D printing files.

While 3D printers play an obvious and enormous role in digital fabrication, the science of materials is one of great study today and of critical importance in making medical models and devices.

Specifications for 3-dimensional printer

Printing settings in Z-Suite program to select the infill density values.

Six different materials were assessed regarding the effects of infill density with a Zortrax M300 Plus:

• ABS
• ULTRAT
• HIPS
• PETG
• PLA
• FLEX

Physical characteristics of materials used in 3-dimensional printing

With Z-suite software designed for the Zortrax printer, the researchers could print with various infill densities, allowing them to make a variety of samples: 4×4×2 cm rectangles made from HIPS and PLA

For the study experiments, samples were created as follows:

“… six printing materials, each at an infill density of 60%. ABS, ULTRAT, HIPS, PETG, PLA, and FLEX had HU values of −535±12, −557±10, −542±7, −508±20, −530±25, and −633±15, respectively. The HU values were similar regardless of the specific density of the materials.”

Hounsfield unit (HU) values of materials used in 3-dimensional printing with infill density of 60%

Correlations between Hounsfield unit (HUs) and infill density values for high impact polystyrene (HIPS) and polylactic acid (PLA) are plotted with dashed lines, respectively. Polynomial fitting curves for these correlations for HIPS and PLA are plotted with solid lines, respectively.

Values of HIPS and PLA were evaluated, with the scientists considering also how long it took to 3D print each material at a specific infill density, as follows:

• Average printing time of 32 minutes with infill density of 10%
• Average printing time of 12 hours and 45 minutes with infill density of 100%

“Considering that the volume of each prepared cube was 32 m³, a printing time of 12 hours and 45 minutes could be considered quite wasteful. Using 100% infill density should therefore be carefully considered while manufacturing patient-specific human phantoms,” concluded the researchers.

“The results suggest that using optimized infill densities will help improve the quality of radiation therapy by producing customized instruments for each field of radiation therapy.”

(a) High impact polystyrene material with infill density values from 10% to 100% and (b) computed tomography (CT) images in coronal view obtained by the Brilliance CT Big Bore™.

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