Tungsten filled 3D printed lung blocks for total body irradiation

Purpose Lung blocks for total-body-irradiation (TBI) are commonly used to reduce lung dose and prevent radiation pneumonitis. Currently, molten Cerrobend containing toxic materials, specifically lead and cadmium, is poured into molds to construct blocks. Here, we propose a streamlined method to create 3D-printed lung block shells and fill them with tungsten ball-bearings (BBs) to remove lead and improve overall accuracy in the block manufacturing workflow. Methods and Materials 3D-printed lung block shells were automatically generated using an inhouse software, printed, and filled with 2-3mm diameter tungsten BBs. Clinical Cerrobend blocks were compared to the physician drawn blocks as well as our proposed tungsten filled 3D-printed blocks. Physical and dosimetric comparisons were performed on a linac. Dose transmission through the Cerrobend and 3D-printed blocks were measured using point dosimetry (ion-chamber) and the on-board Electronic-Portal-Imaging-Device (EPID). Dose profiles from the EPID images were used to compute the full-width-half-maximum (FWHM) and to compare with the treatment-planning-system (TPS). Additionally, the coefficient-of-variation (CoV) in the central 80% of FWHM was computed and compared between Cerrobend and 3D-printed blocks. Results The geometric difference between TPS and 3D-printed blocks was significantly lower than Cerrobend blocks (3D: -0.88±2.21mm, Cerrobend: -2.28±2.40mm, p=0.0002). Dosimetrically, transmission measurements through the 3D-printed and Cerrobend blocks for both ion-chamber and EPID dosimetry were between 42–48%, as compared to the open field. Additionally, CoV was significantly higher in 3D-printed blocks versus Cerrobend blocks (3D: 4.2±0.6%, Cerrobend: 2.6±0.7%, p<0.0001). Conclusions We designed and implemented a tungsten filled 3D-printed workflow for constructing TBI lung blocks, which serves as an alternative to the traditional Cerrobend based workflow currently used in clinics. This workflow has the capacity of producing clinically useful lung blocks with minimal effort in an attempt to facilitate the removal of toxic materials from the clinic.