Surface dose comparison between Acuros XB and Anisotropic Analytical Algorithmfor breast cancer radiotherapy

Abstract

A new algorithm for photon dose calculation, Acuros XB, has been recently introduced in the new version of Eclipse treatment planning, it employs a sophisticated Linear Boltzmann transport equation (LBTE) to account for the effects of heterogeneities in patient dose calculation. The purpose of this research is to compare the surface dose between AAA and the new algorithm Acuros XB in breast cancer radiotherapy techniques. The study was performed for surface dose verification in the homogenous solid water phantom and non-homogeneous CIRS thorax phantom. Moreover, the surface doses of 12 breast conserving surgery cases were investigated with 8 treatment planning techniques, i.e. open field, standard wedged tangent (SWT), electronic compensator (E Comp), field-in-field (FF), tangential intensity modulated radiation therapy (T IMRT), coplanar intensity modulated radiation therapy (CP IMRT), non-coplanar intensity modulated radiation therapy (NCP IMRT) and volumetric modulated arc therapy (VMAT) in Eclipse treatment planning system (TPS) using AAA and Acuros XB. The surface point doses were recorded at tip, medial and lateral sides of the breast at the surface, 4mm, 6mm depth and compared in both algorithms. The surface dose verification in homogeneous phantom showed AAA and Acuros XB calculation were higher than film measurement of 33.32% and 12.31%, respectively. The verification in CIRS phantom illustrated that AAA and Acuros XB were 28.96% and 14.31%, respectively, underestimated dose than film measurement at the surface. For the patient analysis, the tip of the breast showed the highest differences for surface between two algorithms, especially CP IMRT and VMAT techniques. The surface dose differences of the lateral side was much higher than the medial side of the breast. At the deeper depth start from 6mm, both calculation algorithms showed the good agreement approximately 6% for all techniques, which agreed with Akino et al study. It is concluded that the treatment planning system cannot give the accurate dose for surface dose calculation, as verified with the EBT2 film on homogeneous slab phantom and non-homogeneous CIRS thorax IMRT phantom. Acuros XB contributes very high dose differences to the AAA at the surface, especially CP IMRT and VMAT, but comparable at the deeper depth starting from 6 mm. The surface dose for breast radiotherapy depends on the geometry of the structure and treatment techniques used.