Potential of 3D printing technologies for fabrication of electron bolus and proton compensators

Abstract

In electron and proton radiotherapy, applications of patient-specific electron bolus or proton compensators during radiation treatments are often necessary to accommodate patient body surface irregularities, tissue inhomogeneity, and variations in PTV depths to achieve desired dose distributions. Emerging 3D printing technologies provide alternative fabrication methods for these bolus and compensators. This study investigated the potential of utilizing 3D printing technologies for the fabrication of the electron bolus and proton compensators. Two printing technologies, fused deposition modeling (FDM) and selective laser sintering (SLS), and two printing materials, PLA and polyamide, were investigated. Samples were printed and characterized with CT scan and under electron and proton beams. In addition, a software package was developed to convert electron bolus and proton compensator designs to printable Standard Tessellation Language file format. A phantom scalp electron bolus was printed with FDM technology with PLA material. The HU of the printed electron bolus was 106.5 ± 15.2. A prostate patient proton compensator was printed with SLS technology and polyamide material with -70.1 ± 8.1 HU. The profiles of the electron bolus and proton compensator were compared with the original designs. The average over all the CT slices of the largest Euclidean distance between the design and the fabricated bolus on each CT slice was found to be 0.84 ± 0.45 mm and for the compensator to be 0.40 ± 0.42 mm. It is recommended that the properties of specific 3D printed objects are understood before being applied to radiotherapy treatments.

Figure 1

Characterization setup for 3D printed cubes under (a) electron beam with a field projection of $10\times 10\hspace{0.17em}\text{cm}$ cone at 100 cm SSD, and (b) proton monoenergetic pencil beam.

Figure 2

Comparison of the film measurements with the TPS dose calculations for the PLA cube irradiated with 300 MU 12 MeV electron beam. The horizontal planar dose distribution at 3 cm depth underneath the cube (a) on the film and (b) TPS calculation. The vertical dose distribution beyond 3 cm depth under the cube (c) on a film and (d) from TPS calculation. The black line in (c) and (d) marks the 5 cm depth. The color bar shows dose in cGy.

Figure 3

Proton depth0dose curves under monoenergetic pencil beam with and without the 3D printed cubes intercepting the beam. Sample A was the 4 cm polyamide cube, B was the 3 cm PLA cube. Solid lines correspond to measured depth‐dose curves and dashed lines correspond to Monte Carlo‐simulated curves.

Figure 4

3D rendering of (a) electron bolus and (b) proton compensator from the model STL files. The printed (c) electron bolus (d) proton compensator.

Figure 5

Example of a CT slice of the 3D‐printed (a) electron bolus, (b) proton compensator; and the scanned profiles of (c) electron bolus and (d) proton compensator in comparison with the design.