Development and dosimetric verification of 3D customized bolus in radiotherapy

Abstract

Bolus is a tissue equivalent material that is commonly used to reduce the skin-sparing effect in radiotherapy. The commercial flat bolus cannot form perfect contact with the irregular surface of the patient’s skin, resulting in an air gap, especially in irregular surface shape. The purpose of this study was to evaluate the feasibility of two types of silicone rubber bolus, RA-00AB, and RA-05AB that were made as to the fabricated flat and 3D customized bolus using 3D printing technology. The 1 cm thick boluses were made from two types of silicone rubber solutions. The point dose and planar dose differences were evaluated by comparing with virtual bolus using gamma index from SNC-patient software. The physical properties were also evaluated by comparing with a commercial one. For the 3D customized bolus, the bolus shell was designed at the nose, cheek, and neck region from the Fusion 360 program. Then print out the shell with the 3D printer and filled the shell with silicone rubber solution. The dosimetric effect of 3D customized bolus was compared to commercial bolus situation by virtual bolus as a reference. The point dose differences between RA-00AB and RA-05AB silicone rubber model compared with commercial bolus were lesser than 0.4%, while the planar dose differences of both models at 2%/2mmm gamma criteria were the same result more than 99% pass. The thickness, density, Hounsfield unit (HU), and dose attenuation of customized bolus were quite the same as a commercial bolus. When a 3D customized bolus was placed on the RANDO phantom, it showed a very good fit against the irregular surface shape compared with the commercial bolus. Gamma passing rate of 3D customized was higher than commercial bolus for all regions, build-up doses increased and the target volume obviously presented more uniform doses compared to the without bolus situation. A silicone rubber bolus produced the feasible dosimetric properties of a commercial bolus and could save cost when compared to a commercial bolus. The 3D printed customized bolus is a good buildup material and could potentially replace and improve treatment efficiency.