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

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.

A novel approach to embed eye shields in customized bolus on nasal dorsum treatment for electron radiotherapy.

We aim to demonstrate the unique use of embedded lead eye shields in an electron wax bolus when treating the nasal dorsum. A patient presented to the clinic with squamous cell carcinoma of the nasal dorsum requiring treatment with en face electrons. A 3D customized wax bolus was designed and imported into the treatment planning system (TPS) to calculate the dose distribution. Due to high lens dose, the bolus was customized further to create 2 milled open slots in the wax, over the lens of eye, to allow lead sheets totaling 4 mm to be slid into the wax. The patient was brought back to the clinic to be scanned with the wax bolus fitting snugly over the nose, eyes, and cheek regions. The 3D milled insert holes were contoured on the CT in the TPS, assigned HU of 2758, to mimic the lead insertion. The lens dose with lead inserts was compared to the plan without lead insert. To further confirm the lens dose, EBT3 films were placed on the right and left eye under the bolus, and nose dorsum on the first day of treatment. The maximum dose of right lens, as calculated in the TPS with the simulated lead shields in place, decreased from 989.5cGy to 457cGy. The maximum dose of left lens decreased from 1085.4cGy to 501cGy. The dose readings from EBT3 films were in good agreement with the TPS, with deviation of 3.32%, 0.26%, and 3.44% for right lens, left lens, and nose, respectively. Daily positioning deviations compared to the plan were 0.65 ± 0.16cm and 0.63 ± 0.29cm for right eye and left eye, respectively. This novel device demonstrated the feasibility, in terms of dose calculation accuracy in the TPS and fabrication, of using customized bolus with lead inserts to conveniently shield the lens of the eyes in an electron treatment for the nose, enabling a streamlined daily setup.