Dosimetric Comparison of Collapsed Cone Convolution/Superposition and Anisotropic Analytic Algorithms in the Presence of Exaskin Bolus in Radiotherapy

Bolus-type materials are needed in case of superficial lesions radiotherapy. This work determined the dosimetric accuracy of two commercial treatment planning systems (TPS) for calculating photon dose distribution in the presence of eXaSkin bolus.
Dose calculations were performed on collapsed cone convolution/superposition (CCC) and anisotropic analytical algorithm (AAA) using computed tomography (CT) images of heterogeneous CIRS phantom. EBT3 film was used to obtain percentage depth dose (PDD) curves and gamma index was utilized to compare the accuracy of the two algorithms. The passing rate of the global gamma index with the passing criterion of 3mm/3% as the standard criterion was considered 95% in this study.
Surface dose in PDD curves increased in the presence of 0.5 cm thick eXaSkin bolus. The passing rates of gamma index with standard passing criterion between AAA algorithm and EBT3 film measurements without and with bolus were 95% and 95.5%, respectively, while they were equal to 96% and 97.5% for CCC algorithm.
There was a good agreement in dose calculation between AAA and CCC algorithms. Furthermore, eXaSkin bolus increased the surface dose by a factor of 25%.