DEVELOPMENT OF 3D-PRINTED PATIENT SPECIFIC BOLUS FOR CLINICAL USE IN TOTAL SCALP IRRADIATION

Total scalp irradiation (TSI) is a specialized radiation therapy technique that aims to deliver a uniform dose to the entire scalp. Original electron-based TSI techniques had limited homogeneity due to hot and cold spots created at field junctions due to the multiple matched fields that were required to treat the entire scalp. The transition to photon volumetric-modulated arc therapy based TSI techniques has improved homogeneity, to the point where non-conformal bolus is now a limiting factor. Bolus is required to build-up full dose to the scalp surface in total scalp irradiation. Creating bolus that is conformal to the scalp is technically challenging due to the convex curvature of the scalp, and most methods in the literature are laborious yet produce bolus with limited conformality and setup reproducibility. The purpose of this study was to develop and validate the use of patient-specific 3D-printed bolus caps for TSI. 3D-printing materials were studied to find materials suitable for use as a bolus cap. Clinical workflows were developed to 3D-print two bolus caps for an anthropomorphic head phantom: one printed using an in-house 3D printer, and the other using a commercial vendor. CT simulation scans were used to assess bolus cap scalp conformality, and to generate radiation treatment plans. The planned treatment was delivered to the head phantom for both bolus caps, and dosimetric validation was performed using thermoluminescent dosimeters (TLD). The resulting 3D-printed bolus caps had excellent conformality to the phantom scalp, with air gaps of less than 4 mm. Dosimetric measurements demonstrated the bolus caps can generate full build-up to the scalp surface and that measured doses agreed with predicted doses to within 2.4% on average. In conclusion, this study has developed a novel technique to 3D-print highly conformal patient-specific bolus caps that satisfy clinical and dosimetric requirements for total scalp irradiation