Room: Exhibit Hall | Forum 7
Purpose: Bolus is a useful tool for overcoming the skin sparing effects of therapeutic photon beams; however, for complex geometries, planar bolus may leave significant air gaps. Planar bolus is also more optically dense than 3D-printed bolus and introduces potential positioning challenges creating potential for further dosimetric errors. Therefore, we present physical and optical density measurements of 3D-printed bolus versus planar bolus along with quantification of air gaps between bolus and target.
Methods: 3D-printed and planar bolus were simulated with computed tomography (CT) and contoured in Philips Pinnacle treatment planning software; a 1 mm rind was removed from the statistics to discount air/bolus density blurring from image resolution. Physical density parameters of both planar and custom 3D bolus were calculated from CT numbers (electron density) in Pinnacle using the Philips Brilliance CT to density table. Bolus clarity was also calculated from the ratio of detected to incident light. Finally, air gaps were contoured and quantified in Pinnacle to evaluate differences in conformity between planar and 3D bolus.
Results: 3D custom-printed bolusâ€™s density was significantly more uniform (Â±0.019 g/cm3) than planar bolusâ€™s density (Â±0.093 g/cm3) as calculated from CT to density relation. Also, planar bolus showed a precipitous drop in density in horizontal profiles. 3D-printed bolus was found to have approximately ten-fold superior clarity than planar bolus at 1 cm thickness. Finally, maximum bolus-to-skin air gaps were also reduced from approximately 1 cm with planar bolus to 0.6 cm using 3D-printed bolus.
Conclusion: 3D-printed bolus is a useful tool for overcoming skin-sparing for complex geometries as compared to planar bolus. 3D-printed bolusâ€™s custom fit, better uniformity, and lower opacity allow for superior clinical setup with better conformity for complex fields thus potentially leading to superior dosimetric outcomes.