Comparison of doses calculated by anisotropic analytical algorithm and pencil beam convolution in the inhomogeneous tissues

The human body consists of tissues, which have different densities. These inhomogeneous densities effect the dose distributions. In order to get accurate dose distribution in the intensity modulated radiotherapy (IMRT), treatment planning system dose calculation algorithms should model precisely. Dose distributions of Anisotropic Analytical Algorithm (AAA) and Pencil Beam Convolution (PBC) dose calculation algorithms in the inhomogeneous tissues were compared. Furthermore calculated doses were verified as dose measurements using ionization chamber. Moreover, dose profiles and percentage depth dose (PDD) curves created by AAA and PBC were investigated. Whether the amount of tissue volume with air density included by planning target volume has an effect on dose distribution was studied. Calculated organs at risk doses by AAA and PBC were significantly different but clinically negligible. On the other hand, hot spot region was larger in AAA than PBC plans (p=0.005). For homogeneous phantom, calculated and measured doses were not significantly different in AAA plans (p=0.074), in contrast significantly different in PBC plans (p=0.012), all the differences were limited within %3. For inhomogeneous phantom, calculated and measured doses were not significantly different for AAA (p=0.139), significantly different for PBC (p=0.007); this difference was >6%. While there was no significant difference between AAA and PBC created PDDs and dose profiles in the homogeneous phantom, significant difference was seen in the inhomogeneous phantom. Disparity was markedly seen in sharp in the regions outside the ? eld edge. Maximum dose and hot spot region increased with the amount of tissue volume with air density included by planning target volume for both algorithms.