Physical and dosimetric characterization of thermoset shape memory bolus developed for radiotherapy

PURPOSE: We developed a thermoset shape memory bolus (shape memory bolus) made from poly‐ε‐caprolactone (PCL) polymer. This study aimed to investigate whether the shape memory bolus can be applied to radiotherapy as a bolus that conformally adheres to the body surface, can be created in a short time, and can be reused. METHODS: The shape memory bolus was developed by cross‐linking tetrabranch PCL with reactive acrylate end groups. Dice similarity coefficient (DSC) was used to evaluate shape memory characterization before deformation and after restoration. In addition, the degree of adhesion to the body surface and crystallization time were calculated. Moreover, dosimetric characterization was evaluated using the water equivalent phantom and an Alderson RANDO phantom. RESULTS: The DSC value between before deformation and after restoration was close to 1. The degree of adhesion of the shape memory bolus (1.9%) was improved compared with the conventional bolus (45.6%) and was equivalent to three‐dimensional (3D) printer boluses (1.3%–3.5%). The crystallization time was approximately 1.5 min, which was clinically acceptable. The dose calculation accuracy, dose distribution, and dose index were the equivalent compared with 3D boluses. CONCLUSION: The shape memory bolus has excellent adhesion to the body surface, can be created in a short time, and can be reused. In addition, the shape memory bolus needs can be made from low‐cost materials and no quality control systems are required for individual clinical departments, and it is useful as a bolus for radiotherapy.