Towards a customizable 3D printed heterogeneous radiotherapy phantom for treatment quality assurance: Fabrication, characterization, and dosimetry

Additive Manufacturing (AM) also known as three-dimensional (3D) printing is a construction procedure involving material deposition in layers based on a computer aided design (CAD) model. AM is an active field of research with a view to manufacturing patient specific equipment, which is highly desired in radiotherapy. Current methods compare measurements in commercially available single-material phantoms to treatment simulations based on the patient’s geometry. However, commercial phantoms offer limited geometry, tissue-equivalence, and dosimetry capabilities. This restricts the accuracy of approximating the in-vivo dose of the patient. This study provides a preliminary characterization data of selected AM materials for clinical linear accelerator radiotherapy. The AM materials used to print test objects can simulate tissues from near adipose up to near inner bone-equivalent. Fifteen AM materials were used to fabricate test objects using material extrusion and vat photopolymerization techniques. A variety of fabrication parameters and challenges were investigated to check its relationship of the radiological characteristics with the printed object. In addition, soft tissue equivalent filaments were used to fabricate a 1 mm thick slab phantom for comparison with a water equivalent RW3 slab phantom under radiotherapy delivery beams using 6 & 10 MV photons as well as 6, 9, 12, 15, and 18 MeV electrons. The 3D AM printed slab phantoms used in the photon dosimetric evaluation for 6 and 10 MV X-rays, show precise agreement the commercial water equivalent RW3 material, with a maximum difference of 0.61%. The five electron energies have overall a very good agreement, with < 3% difference between the TPS calculated dose. However, there is an observable variation in the 12 MeV and 15 MeV irradiation of about < 5% difference for the eSilk PLA and PLA+. Our preliminary results indicate AM materials will be useful for fabricating low-cost, highly customizable radiotherapy phantoms for both clinical and preclinical research.