Electron Backscatter Dose Reduction Using 3D-Printed Aluminum
Abstract
Purpose
Aluminum (Al, 2.7 g/cc) can be used with internal lead shielding to reduce backscattered dose to superficial targets, particularly in superficial lip cancers. Cutting and molding an Al sheet to comfortably fit inside the mouth of the patient is a challenge. This work tests the electron backscatter reduction efficacy of aluminum-polylactic acid filament (Al-PLA, 1.45 g/cc), which can be 3D-printed to conform to the patient dental contour.
Methods
The Al-PLA prints were produced at 250C nozzle temperatures on the commercially available Bambu H2Dpro. For dosimetry measurements, EBT4 GAFchromic film was calibrated between 10 MU and 1000 MU for 9 MeV electrons. Backscatter reduction was tested on both Al and Al-PLA sheets with thicknesses of 1.0 mm, 2.0 mm, and 3.0 mm, measuring the upstream-of-lead and downstream-of-lead dose for tissue depths between 2.5 cm to 3.5 cm with lead thickness of 4.8 mm, reported relative to a 1.6 times backscatter factor.
Results
For 9 MeV electrons at 2.5 cm tissue depth, the backscatter dose reduction with [1 mm, 2 mm, 3 mm] Al was [14%, 25%, 29%] and Al-PLA was [9%,14%, 20%]. At 3.0 cm tissue depth the reduction with Al was [19%, 27%, 30%] and Al-PLA was [13%, 23%, 11%]. At 3.5 cm tissue depth the reduction with Al was [27%,34%,36%] and Al-PLA was [2%, 7%, 14%]. Downstream dose was consistently near 0 cGy.
Conclusion
The same thickness of Al-PLA did reduce the backscattered dose to half the efficacy of Al, requiring roughly double the thickness. The filament can be used for patient-specific shielding using the patient contours acquired from simulation, however challenges remain with the consistency of printing using commercially available 3D printers and limitation of space where internal shielding will be used.