SU‐C‐BRB‐06: Utilizing 3D Scanner and Printer for Dummy Eye‐Shield: Artifact‐Free CT Images of Tungsten Eye‐Shield for Accurate Dose Calculation

Abstract

Purpose:To evaluate the effect of a tungsten eye‐shield on the dose distribution of a patient.Methods:A 3D scanner was used to extract the dimension and shape of a tungsten eye‐shield in the STL format. Scanned data was transferred into a 3D printer. A dummy eye shield was then produced using bio‐resin (3D systems, VisiJet M3 Proplast). For a patient with mucinous carcinoma, the planning CT was obtained with the dummy eye‐shield placed on the patient's right eye. Field shaping of 6 MeV was performed using a patient‐specific cerrobend block on the 15 × 15 cm2 applicator. The gantry angle was 330° to cover the planning target volume near by the lens. EGS4/BEAMnrc was commissioned from our measurement data from a Varian 21EX. For the CT‐based dose calculation using EGS4/DOSXYZnrc, the CT images were converted to a phantom file through the ctcreate program. The phantom file had the same resolution as the planning CT images. By assigning the CT numbers of the dummy eye‐shield region to 17000, the real dose distributions below the tungsten eye‐shield were calculated in EGS4/DOSXYZnrc. In the TPS, the CT number of the dummy eye‐shield region was assigned to the maximum allowable CT number (3000).Results:As compared to the maximum dose, the MC dose on the right lens or below the eye shield area was less than 2%, while the corresponding RTP calculated dose was an unrealistic value of approximately 50%.Conclusion:Utilizing a 3D scanner and a 3D printer, a dummy eye‐shield for electron treatment can be easily produced. The artifact‐free CT images were successfully incorporated into the CT‐based Monte Carlo simulations. The developed method was useful in predicting the realistic dose distributions around the lens blocked with the tungsten shield.