Purpose:Three-dimensional dose verification can detect dose difference between planned and delivered dose distribution.The aim of the study is to extend a previous in-house developed three-dimensional dose reconstructed model in homogeneous phantom to situation in which tissue inhomogeneities are present.Methods:The method was based on the portal grey images from an electronic portal imaging device(EPID)and the relationship between beamlets and grey-scoring voxels at the position of the EPID.The relationship was expressed in the form of grey response matrix that was quantified using thickness-dependence scatter kernels determined by series of experiments.From the portal grey-value distribution information measured by the EPID the two-dimensional incident fluence distribution was reconstructed based on the grey response matrix using a fast iterative algorithm.The accuracy of the approach was verified using a four-field intensity modulated radiotherapy(IMRT)plan of a lung cancer in anthropomorphic phantom.Each field had between twenty and twenty-eight segments and was evaluated by comparing the reconstructed dose with the measured dose.Results:The gamma-evaluation method was used with various evaluation criteria of dose difference and distance-to-agreement:3%/3mm and 2%/2 mm.The dose comparison for all irradiated fields showed a pass rate of 100%with the criterion of 3%/3mm and a pass rate of higher than 92%with the criterion of 2%/2mm.Conclusion:Our experimental results demonstrated that our method was capable of accurately reconstructing three-dimensional dose distribution in the presence of inhomogeneities.Using the method,the combined planning and treatment delivery process was verified,offering an easy tool for the verification of complex treatments.