Additive Manufacturing Technology in Fabricating Tissue-Equivalent Materials and Dosimetry Equipment for Advanced Radiotherapy Medical Physics Application

<p dir="ltr">Radiation therapy technology advances greatly in the past years because of the development in engineering and computing. This results in an improved dose delivery while decreasing the possibility of treatment complications. Given the increasing complexity and variety of treatment machines and techniques, an improvement in the quality assurance equipment should be considered. Conventional phantom equipment used in radiation therapy are commonly limited to simplified designs and homogenous characteristic. With the medical trend transitioning into personalized treatment, it is important to consider patient-specific quality assurance and customizable dosimetry equipment.</p><p dir="ltr">Three-dimensional (3D) printing or additive manufacturing (AM) is an advanced technology used to manufacture products based on computer-aided design models using a unit material that allows customizable, and patient-specific fabrication. Due to its advantages compared to traditional manufacturing such as design flexibility and multimaterial manufacturing, it has become popular in different industries and fields including medical physics. Bioprinting is another innovative 3D printing technique that uses bioengineering methods to fabricate 3D biological constructs using biomaterials and cells. It can create tissue and tumor constructs that closely mimic some of the structural characteristics and physiological responses of a real tissue and tumor.</p><p dir="ltr">This study characterized the radiological properties and other features of various additive manufacturing technologies and materials such as polymers, ceramics, metals, and hydrogels. Various 3D printed phantoms were fabricated such as a Computed Tomography (CT)-Electron Density phantom, a pediatric head phantom, a rat phantom, and an adult head phantom. Radiological imaging and therapy modalities were used in characterizing different AM materials and phantoms such as clinical CT, synchrotron CT, clinical linear accelerator (Linac), and synchrotron broadbeam and microbeam radiotherapy. Furthermore, the applications of 3D bioprinting in the fabrication of 3D in-vitro brain cancer tumor (glioma) constructs were investigated for synchrotron microbeam radiation therapy experiments. A Gelatin Methacryloyl (GelMA) and a compact 3D REDI bioprinter were used in fabricating bioprinted brain tumors.</p><p dir="ltr">The CT number and attenuation measurements were utilized for tissue-equivalence characterization and printing evaluation. In addition, treatment beams were delivered to the 3D printed materials and phantoms to assess its capabilities as dosimetry equipment. Different dosimeters were used which includes an ionization chamber, microDiamond detector, radiochromic films, and a silicon single strip detector. Furthermore, a validated Geant4 Monte Carlo simulation and a treatment planning system were used to verify the measured doses with calculations for synchrotron radiotherapy and Linac radiotherapy, respectively. For bioprinting experiments, a cell viability assay and a fluorescence imaging method were performed to assess the biological effect of synchrotron radiotherapy delivery. The response of 3D bioprinted tumors was compared to a cell monolayer culture and a 3D spheroid culture.</p><p dir="ltr">The results of this study provided further characterization data, 3D printed phantom fabrication protocols, and 3D bioprinting methods which are important in establishing guidelines in using 3D printing technology for advanced medical radiation physics and radiobiology applications. Overall, this research project demonstrated the capabilities of AM in fabricating customizable, and radiologically tissue equivalent medical physics dosimetry equipment.</p>