Session Item

The work aims to define water-equivalent 3D printing parameters for patient-specific bolus and to evaluate the use of 3D printed bolus on an anthropomorphic phantom.

17 slabs of 10×10×1 cm3 with different printing orientation, infill patterns, infill densities and layer thicknesses were printed with brick red Z-PLA-Pro (Zortrax) on a Zortrax M300 Dual 3D printer.

For film dosimetry, the samples were first CT scanned (Philips Brilliance 64) with 5cm backscattered Plastic Water DT plates (CIRS) under them and images were transferred to the TPS (Philips Pinnacle v16.2). 2 Gy was planned using 6 MV photon beam on the TPS. The electronic density of all the samples was overridden to 1 g/cm3. The homogeneity and dose distributions were analyzed according to the standard deviation and the average value of measured dose.

The clinical use of 3D printed bolus has been tested with an anthropomorphic phantom (STEEV, CIRS). Several boluses with different printing parameters were printed and the one with the highest printing quality was used and compared with a wax bolus, a standard bolus and without bolus. A treatment of 2Gy on a superficial tumor on the nose was planned for all bolus configurations.

Finally, the STEEV phantom was irradiated with film fixed on the nose surface.

The film tests showed good correlation between physical density and dose delivered. Physical density was influenced by infill pattern, infill density, printing orientation and layer thickness. All slabs with infill density ≥ 70% had standard deviation of measured dose similar to the homogenous plastic water and thus inner inhomogeneity could be ignored; grid pattern was chosen because of shorter printing time. Dose difference between slabs printed in horizontal and vertical direction was below 5% and ignorable. 0.2 mm layer thickness was chosen for higher printing quality. The PLA-Pro sample with grid pattern, horizontal orientation, 90% infill and 0.2mm layer thickness was the most similar to plastic water with dose difference less than 3%.

The 3D printed bolus on STEEV phantom showed good treatment result with an average dose of 200.6 cGy on the surface, which was much better compared to the phantom without bolus (161.0 cGy). The average doses on the surface of the wax bolus and the standard bolus were below expectation (193.0 cGy and 188.0 cGy respectively)

The optimal printing parameters were defined for patient-specific 3D-printed bolus with PLA-Pro material and the M300 Dual printer. Grid pattern, 0.2 mm layer thickness and 90% infill density were chosen for further use.

The 3D printed bolus showed good agreement between calculated and measured dose. The clinical use is thus promising for 3D printed bolus.