SU‐E‐J‐200: A Dosimetric Analysis of 3D Versus 4D Image‐Based Dose Calculation for Stereotactic Body Radiation Therapy in Lung Tumors

Abstract

Purpose:To evaluate the dosimetric difference between 3D and 4Dweighted dose calculation using patient specific respiratory trace and deformable image registration for stereotactic body radiation therapy in lung tumors.Methods:Two dose calculation techniques, 3D and 4D‐weighed dose calculation, were used for dosimetric comparison for 9 lung cancer patients. The magnitude of the tumor motion varied from 3 mm to 23 mm. Breath‐hold exhale CT was used for 3D dose calculation with ITV generated from the motion observed from 4D‐CT. For 4D‐weighted calculation, dose of each binned CT image from the ten breathing amplitudes was first recomputed using the same planning parameters as those used in the 3D calculation. The dose distribution of each binned CT was mapped to the breath‐hold CT using deformable image registration. The 4D‐weighted dose was computed by summing the deformed doses with the temporal probabilities calculated from their corresponding respiratory traces. Dosimetric evaluation criteria includes lung V20, mean lung dose, and mean tumor dose.Results:Comparing with 3D calculation, lung V20, mean lung dose, and mean tumor dose using 4D‐weighted dose calculation were changed by −0.67% ± 2.13%, −4.11% ± 6.94% (−0.36 Gy ± 0.87 Gy), −1.16% ± 1.36%(−0.73 Gy ± 0.85 Gy) accordingly.Conclusion:This work demonstrates that conventional 3D dose calculation method may overestimate the lung V20, MLD, and MTD. The absolute difference between 3D and 4D‐weighted dose calculation in lung tumor may not be clinically significant.This research is supported by Siemens Medical Solutions USA, Inc and Iowa Center for Research By Undergraduates