Purpose:To evaluate dosimetric uncertainty in 4D dose calculation for lung cancer patients using three different temporal probabilities.Methods:The impact of temporal probability, defined as the fraction of time a patient spends in each respiratory amplitude, was evaluated in nine lung cancer patients. For each patient, 4D dose was computed using 4DCT and three temporal probability distributions: 1) uniform distribution, 2) sinusoidal distribution, and 3) patient‐specific distribution. To calculate 4D dose, the dose for each of 10 binned CTs was first computed using the same planning parameters as those used in the breath‐hold CT. Next, deformable image registration was used to deform the dose of each binned CT to the breathhold CT using the deformation map between each binned CT and the breathhold CT. Finally, 4D dose volume was computed by summing the 10 deformed doses using corresponding temporal probabilities. In this study, 4D dose calculated from patient‐specific temporal probabilities was used as the ground truth. Dosimetric comparison included: 1) 3D gamma (3% dose difference, 3mm distance to agreement tolerance), 2) mean tumor dose (MTD), 3) mean lung dose (MLD), and 4) lung V20.Results:For all patients, both uniform and sinusoidal dose distributions were found to have an average gamma passing rate >99% for both lung and PTV volume. Compared with 4D dose calculated using the patient respiratory trace, uniform distribution and sinusoidal distribution showed a percentage difference on average of ‐0.1±0.6% and ‐0.2±0.4% in MTD, ‐0.2±2.0% and ‐0.2±1.3% in MLD, 0.9±2.8% and ‐0.7±1.8% in lung V20, respectively.Conclusion:Both uniformly and sinusoidally‐distributed temporal probabilities can be used to approximate 4D dose calculation. The dosimetric difference among the three temporal probability distributions is not clinically significant.This research is supported by Siemens Medical Solutions USA, Inc

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