Master of Science (MS)
Physics and Astronomy
Background: Phantoms have been in use in medical and health physics for decades, serving as a surrogate for human tissue in several different applications. In radiation dose measurements, anthropomorphic phantoms are designed with tissue substitute materials to mimic both the elemental compositions and anatomical structures of the human body. In some cases the performance of anthropomorphic phantoms for personalized measurements is severely limited by the use of reference anatomy in the geometric design. 3D printing could potentially be used to overcome some of these shortcomings by enabling rapid fabrication of personalized phantoms for individual patients based on radiographic imaging data. The aim of this work is to determine whether 3D-printed phantoms are a feasible means of performing patient-specific dosimetric measurements for electron beam radiotherapy. Methods: We measured dose distributions from 6 to 20 MeV electron beams impinging on a variety of materials and geometries to determine the radiological properties of 3D printed phantoms. The water equivalent thickness of homogeneous molded and printed slabs were determined from depth dose measurements. Molded and Printed anthropomorphic slabs were compared for equivalency in electron beam penetration range properties using gamma index analysis with the criteria of 3% dose difference or 3 mm distance to agreement. Last, a personalized head phantom was printed and compared with a reference phantom using gamma index analysis for use in electron beam dose calculations using a treatment planning system. Results: The printed personalized phantom provided superior dosimetric accuracy compared to the molded reference phantom. Personalized 3D printed radiotherapy phantoms achieved a pass rate of greater than 60% for electron beam radiotherapy treatments using 16 and 20 MeV electron energies. Conclusion: Creating personalized phantoms using 3D printing techniques is a feasible way to substantially improve the accuracy of dose measurements of therapeutic electron beams. Further improvements are necessary in order to increase the dynamic range of mass densities that are achievable with printing, e.g., low density lung and high density bone.
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Halloran, Andrew Michael, "Dosimetric Advantages of Personalized Phantoms for Quality Assurance and Research in Radiation Dose Measurements" (2015). LSU Master's Theses. 1227.