Development of an anthropomorphic simulator based on 3D printing for dosimetry in eye radiotherapy

The use of radiotherapy for treatment of ocular tumors is a common fact. Ciliary body, choroid and iris melanomas are the most common malignant tumors in adults among all melanomas. In addition, other types of carcinomas have a high probability of metastasis in ocular structures. The therapeutic dose for head and neck tumors is often restricted by the tolerance of the optical apparatus. The use of anthropomorphic simulators to study the dose distribution in biological tissues is a practice widely used in medical physics. These must have similar characteristics of interaction between radiation and tissue, as well as from a geometric point of view. Commercial anthropomorphic simulators, in general, do not reproduce optical apparatus details and do not provide the insertion of dosimeters in this region. The objective of this work was to build a simulator using 3D printing, to be inserted in the anthropomorphic simulator ATOM®, which would allow the dosimetry of the organs associated with the optical apparatus. In this work, lactic polyacid (PLA) and mixtures of calcium sulfate and sodium chloride were studied, these materials were validated as soft tissue and bone tissue simulators respectively for 6 MeV beams. Chemical composition, apparent density, electronic density, mass attenuation coefficient, electron mass stopping power, depth dose and Hounsfield unit were the quantities studied. For PLA, both the mass attenuation coefficient and the stopping power for electrons obtained differences of less than 5% when compared to equivalent tissue materials already established in the literature (PMMA and solid water), for energies above 0.1 MeV. specific printing conditions, PLA parts filled with approximately 85% have the same depth dose profile as solid water. For the compounds of calcium sulfate and sodium chloride, the mass attenuation coefficient and the braking power for electrons showed discrepancies less than 2% for energies between 1 and 10 MeV. The results of density and relative electronic density agree and indicate that the compound with 46% calcium sulfate is the closest to the values of the ATOM® anthropomorphic simulator. We performed the dosimetry using micro TLD LiF-100 dosimeters. Doses measured by dosimeters in the region of the target volume differed about 2% from the planned, proving the feasibility of using the produced simulator. (author)