Calculation of absorbed dose in lung tissue equivalent and compared it with prediction of a treatment planning system using Collapsed Cone Convolution algorithm

External radiotherapy is used for treatment of various types of cancers. Due to the impossibility of measuring the absorbed dose delivered to different organs during irradiation, treatment planning systems (TPSs) have been utilized for calculation of absorbed dose before a radiotherapy procedure. Thus, the accuracy and precession of the TPS is essential.The aim of this study is investigation of accuracy the TPS based on Collapse Cone Convolution (CCC) algorithm in a lung tissue equivalent material. The charge generated in the sensitive volume of PTW-30013 ionization chamber in water and lung tissue equivalent phantoms placed in the radiation fields of Primus 6MV linac was calculated using MCNP.4C code and in the ratio of generated charge in this phantom was determined. To validate the simulations, the ratio of generated charge in sensitive volume of ionization chamber in mentioned phantoms was determined experimentally. The agreement between the calculations and measurement confirm the simulation method. The calculated absorbed dose delivered in the lung tissue equivalent material for 200 MU radiation was 154.99 cGy using simulations. The CCC algorithms predicted this value as 163.98 cG. As well as, the absorbed dose in different depths was measured using GR-200 Dosimeters. The relative differences between the values obtained by simulation and CCC algorithm and between the results of TLD measurements and CCC algorithms are more than 5.5% and 14%, respectively. So, by considering the acceptable uncertainties suggested by ICRU for TPS algorithms and the results of this work, it can be concluded that, the CCC algorithm is not sufficiently accurate to determine of absorbed dose delivered to tissues with density lower than water.