A Comparison between Three-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy, and Volumetric-Modulated Arc Therapy Techniques for Stereotactic Body Radiotherapy of Lung Tumors

Introduction: The aim of this study is to dosimetrically compare 3D CRT, IMRT, and VMAT techniques that employ coplanar and non-coplanar beams for the SBRT of lung tumors. Methods and Materials: Nine (n = 9) consecutive SBRT lung patients with ten tumor sites who were previously treated at our institution were selected for this study. Six (n = 6) treatment plans were created for each PTV: 1 coplanar and 1 non-coplanar 3D CRT, IMRT, and VMAT such that 98% of PTV received 100% of prescription dose, Rx of 50 Gy in 5 fractions. The data collected from each plan included the conformity index, R50%, and homogeneity index of the target as well as the volume of normal tissue irradiated by 5 Gy, 25 Gy isodose lines, V5 and V20 of total lung, and maximum dose to organs at risk. Beam angles and arc lengths were chosen in order to achieve the lowest total lung V5, V20 and R50% values. Results: According to the observed data, the mean total lung V5 and V20 values were lowest for the non-coplanar VMAT plans, but were not statistically different from the other planning techniques. Conformity values were similar for the IMRT and VMAT plans, and significantly lower than the 3D CRT plans. R50% values were lowest for the VMAT plans and significantly lower than both IMRT and 3D CRT plans in both coplanar and non-coplanar beam arrangements. However, dose homogeneity in the PTV is significantly higher in the IMRT coplanar plans than the corresponding 3D CRT and SmartArc (SA) coplanar plans. Coplanar VMAT plans were able to produce a significant 35.5% reduction in the maximum cord dose than coplanar 3D CRT plans (p-value < 0.03). VMAT plans also reduce the volume of the normal tissue irradiated to high doses, but the reduction is insignificant. Conclusion: Overall, the VMAT plans were able to produce highly conformal plans. No single planning technique can outclass the others in all of the SBRT planning indices significantly and a thorough review of each patient plan is needed.