Comparison of robotic arm linear accelerator device used in treatment planning monte carlo calculations and ray tracing algorithm

In this study, we aimed to compare Monte Carlo and Ray Tracing calculation algorithms used in the robotic arm linear accelerator therapy planning. Different phantom sets were compared using Ray Tracing and Monte Carlo calculation algorithms of Cyberknife treatment planning system Multiplan. These calculation algorithms were also compared in 10 non-small cell lung cancer patients previously treated treatment plans with Cyberknife Stereotactic Radiotherapy. Three different phantom sets were created to the impact of homogeneous and heterogeneous media on treatment planning algorithms. Monte Carlo algorithm has been calculated in phantom set with %1 uncertanity. All treatment plans have been made using similar target coverage and normalization values for both algorithms. Monte Carlo algorithm was also compared for %0.5, %1 and %2 uncertanity values. Main objective is in this study was comparision of CI, HI target coverage values, MU's, hotpoint values, spinal cord and lung doses. Our results have shown a difference of %2 in homogeneous media phantom sets for two algorithms. Furthermore, in heterogeneous media which has more air density, both algorithms differ approximately ±% 3. When patient treatments plans compared, there is %14 diffrence in target coverage between RAT and MC algorithms. Total dose calculated as 54 Gy with Ray Tracing algorithm was found be 46.5 Gy when Monte Carlo algorithm was used. Normalization value of MC algorithm is decreased %5 to achieve the same coverage value of Ray Tracing algorithm. There are significant differences in calculation times and critical organ doses for different uncertanity values. There is no statistical significance on spinal cord values between different uncertanity values (p=0,232). When we look at irridiated and contralateral lung, we have found statistical significance (p = 0,001) between two algorithms. When same target coverage is used for RAT and MC calculation treatments, statistically significance was observed for spinal cord values (p = 0,028), but when same normalization value was used statistical significance was disappeared (p = 0,508). Target coverage values was also same with siggnificant difference, for maximum lung dose (p = 0.037) and for minimum lung dose (p = 0.015). When the normalization values were same a significant difference, was found for maximum dose at the ipsilateral lung (p = 0.007) and for volume which receives 20 Gray dose (V20) (p = 0.024) and for the minimum (p = 0.011) and mean contralateral lung dose (p = 0.011). . Key words : Monte Carlo, Ray Tracing, Cyberknife, Uncertainity