Comparison of Pencil beam, Collapsed cone and Monte-Carlo algorithm in radiotherapy treatment planning for 6 MV photon

Treatment planning system calculations in inhomogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. In this study, three different dose calculation algorithms, pencil beam, collapsed cone, and Monte-Carlo, provided by our planning system were compared to assess their impact on the three-dimensional planning of lung and breast cases. A total of five breast and five lung cases were calculated using the PB, CC, and MC algorithms. Planning treatment volume and organs at risk delineation was performed according to our institutions protocols on the Oncentra MasterPlan image registration module, on 0.3 to 0.5 cm computed tomography slices taken under normal respiration conditions. Four intensity-modulated radiation therapy plans were calculated according to each algorithm for each patient. The plans were conducted on the Oncentra MasterPlan and CMS Monaco treatment planning systems, for 6 MV. The plans were compared in terms of the dose distribution in target, OAR volumes, and monitor units. Furthermore, absolute dosimetry was measured using a three-dimensional diode array detector to evaluate the dose differences in a homogeneous phantom. Comparing the PB, CC, and MC algorithms planned dose distribution, the PB algorithm provided adequate coverage of the PTV. The MUs calculated using the PB algorithm was less than those of the other algorithms. The MC algorithm showed the highest accuracy in terms of the absolute dosimetry. Differences were found when comparing the calculation algorithms. The PB algorithm estimated higher doses for the target than the CC and MC algorithms. The PB algorithm actually overestimated the dose compared with those calculated by the CC and MC algorithms. The MC algorithm showed better accuracy than the other algorithms.