Effectiveness Of A 3d-Printed Bolus With Gel And Silicon Materials For An Irregularly Shaped Skin Surface

A bolus is used to complement the decrease in surface dose due to build-up during radiotherapy for skin lesions. A commercially available bolus is often used, but in cases of an uneven shape, it is difficult to bring the tumor and bolus close to each other, possibly resulting in a layer of air that can cause a decrease in the surface dose. Research on stereoscopic bolus creation using a 3D printer has been carried out in recent years,but the bolus is usually hard because acrylonitrile butadiene styrene (ABS) and polylactide (PLA) are generally used as 3D printer materials. Adhesion of the bolus was difficult if there was an air layer between the surface of the body and the 3D-printed bolus. We therefore made a personal specific 3D-printed bolus using gel and silicon, which are flexible materials with good adhesion, and we evaluated dosimetric characteristics for photon and electron radiotherapy. In order to create a personal specific bolus, we created a gel bolus using a 3D gel printer which is the world's first technology (gel bolus is a high-strength gel 3D gel printer made by UV irradiation into unreacted solution), and a silicone bolus was made by making a bolus shape with plaster and pouring the silicon material into it. In order to determine whether the qualitative characteristics and deep dose characteristics are equivalent to those of existing boluses, we first compared the CT values of the boluses and compared the the degrees of adhesion to the surface. Next we created treatment plans for water-equivalent phantoms with a gel bolus, a silicon bolus, a commercial bolus, a virtual bolus and no bolus, and then we compared the percentage depth dose (PDD) by X-ray and electron beam irradiation. We also compared the absolute doses by chamber measurements. In the comparison of CT values of the materials, the value of silicone was high (130 HU) and a gel and a commercial bolus were water equivalent. The air gaps were lesser with the 3D-printed bolus than with the commercial bolus. A comparison of PDD curves showed that the surface dose increased compared to that without a bolus for each bolus and that both the gel bolus and silicone bolus were equivalent to the commercial bolus. Even in absolute dose comparison by chamber measurements, both the gel bolus and silicone bolus were equivalent to the commercial bolus. The physical properties of 3D-printed boluses using gel and silicone materials are equivalent to those of a commercial bolus and adhesion of the 3D-printed boluses an irregularly shaped skin surface is superior to that of a commercial bolus.