Author: Emily Helen Hayes, Luke Maloney 👨🔬
Affiliation: University of Florida 🌍
Purpose: To determine the dosimetric water equivalency of polylactic acid (PLA) and commercial 3D printing resin using electron stopping power as a surrogate, for use in radiochromic film calibration and phantom development. The water equivalency of PLA and resin has been investigated in diagnostic regimes for photons, but dosimetric equivalency has not been well-established.
Methods: A phantom with variable depth was printed to investigate dosimetric equivalency of printed materials. The phantom consists of cylinders with 25mm radii and varying heights (2mm to 20mm). A lateral scatter block (100mm x 100mm x 50mm) encases the cylinders, with dimensions determined by practical electron range. Components were printed in PLA and resin using filament and stereolithography printers. Phantoms were irradiated with 6 MeV electrons at variable film depth using a linear accelerator. Films were scanned after 48 hours to determine optical density. Calibration fits were of the form d=a+b/(D-c), where d is depth, D is dose. Percent depth dose curves (PDDs) were evaluated for each material and compared to that of water. The ratio of the slope of the linear part of the PDD to that of water is compared to the specific gravity of each material to demonstrate dosimetric equivalence.
Results: Examination of the PDD curves indicates that the depth of maximum dose (dmax) of resin and PLA occur at 12.5mm and 10mm, respectively, compared to 13mm in water. The doses at dmax are 199.2cGy for resin, 210.3cGy for PLA and 200cGy for water. The “percent dosimetric difference” with respect to water is 2.26% for PLA and –0.87% for resin.
Conclusion: This work enhances clinical accuracy by enabling greater flexibility in calibration of film and development of patient-specific phantoms. This work will discuss a device enabling single-irradiation calibration for film batches, simplifying workflow for physicists using film for in vivo measurements.