The Effect of Pencil Beam, Collapsed Cone, and Monte Carlo Algorithms on Dose-Volume Parameters in Esophagus Cancer: The Digital Phantom Study

OBJECTIVE The aim of the study was to compare the effects of three different planning algorithms in esophageal cancer on treatment and normal tissues according to different energy and field angles. METHODS In this study, a tumor volume was determined in the middle esophagus in the digital phantom. By targeting this tumor volume, a three-dimensional conformal radiotherapy treatment plan was created and dose-volume histograms (DVH) were compared according to the Pencil Beam, Collapsed Cone,and Monte Carlo algorithms. The total dose was determined as 5040cGy (1.8 Gy/fraction). In DVH; mean planning target volume dose was evaluated as D50, D98, D2; mean dose for the heart as V5, V30; mean dose for lung as V5, V20; and also the maximum dose (Dmax) for the spinal cord and homogeneity index were assessed. A total of 18 plans created at the same energy levels (6 and 18MV) and angles (3, 4, and 5 fields) were compared using these three different algorithms. RESULTS Different algorithms created significant differences with the same energy and same field angles as we expected. Especially when considered in terms of normal tissues, the remarkable difference was in the heart (Dmean, V5), lung (Dmean, V5, V20), and spinal cord Dmax values. There were also differences in algorithms between PTV dose values. We found that with the increase in the energy level and field, the dose differences between algorithms significantly reduced. CONCLUSION Variations between algorithms that may occur due to the difference in density between tissues in the thoracic region should be taken into consideration.