Innovation of inexpensive customized bolus in radiotherapy from 3D printer using silicone bolus

Abstract

Introduction: Bolus is a water-equivalent material that is commonly used to increase the buildup region dose and compensate for missing tissue in radiotherapy. The commercial superflab bolus is quite expensive and cannot perform the perfect contact with the irregular shape of the patient’s surface. The aim of this study was to study the characteristics of in-house silicone rubber bolus to apply in radiotherapy. Methods: The methods start with mixing the RA-00A and RA-00B solutions into a homogeneous substance. The solutions were poured into the holder to create a 1 cm silicone rubber thickness with the size of 30x30 cm^2. The physical properties of thickness, density, and hardness were evaluated and compared with the commercial bolus. A piece of silicone rubber bolus was scanned by a CT simulator. The CT images of the silicone rubber bolus were used to evaluate the Hounsfield unit (HU) and the dose attenuation was also evaluated in the Eclipse treatment planning system. The 3D shape of the nose was created as a 3D customized bolus using 3D printed technology. Results: We found that the commercial bolus and the customized one showed a thickness of 1.05±0.00 cm and 1.07±0.01 cm, density of 1.03 and 0.99 g/cm3, and hardness of 2.5 HA and 1.5 HA, respectively. The HU of commercial bolus and customized bolus were -124±63.3 and -73±42.5, respectively. The surface dose differences between silicone bolus and commercial bolus of 6 MV, 10 MV, 6 MeV, and 9 MeV were 0.4%, 0.9%, 0.7%, and -0.4%, respectively. The silicone bolus can increase surface doses in clinics of 68.5%, 67.1%, 17.7%, and 7.4% compared to the amount of radiation at the surface without the bolus, it will be 30,23.1,81.5, and 86.9 for 6 MV, 10 MV, 6 MeV, and 9 MeV, respectively. comparable to the result from a commercial superflab bolus. The 3D customized bolus presented the perfect fit to the irregular surface shape phantom and significantly increased the buildup region dose. Conclusion: Silicone rubber is an alternative material that can replace commercial bolus because of the comparable properties with more than 20 times cheaper prices. It can also be molded into 3D shapes according to organs and lesions.