Abstract
In the traditional two-step procedure used in intensity-modulated radiation therapy, fluence map optimization (FMO) is performed first, followed by use of a leaf sequencing algorithm (LSA). By contrast, direct aperture optimization (DAO) directly optimizes aperture leaf positions and weights. However, dose calculation using the Monte Carlo (MC) method for DAO is often time-consuming. Therefore, a rapid DAO (RDAO) algorithm is proposed that uses a dose influence matrix based piecewise aperture dose model (DIM-PADM). In the proposed RDAO algorithm, dose calculation is based on the dose influence matrix instead of MC. The dose dependence of aperture leafs is modeled as a piecewise function using the DIM. The corresponding DIM-PADM-based DAO problem is solved using a simulated annealing algorithm.The proposed algorithm was validated through application to TG119, prostate, liver, and head and neck (H&N) cases from the common optimization for radiation therapy dataset. Compared with the two-step FMO–LSA procedure, the proposed algorithm resulted in more precise dose conformality in all four cases. Specifically, for the H&N dataset, the cost value for the planned target volume (PTV) was decreased by 32%, whereas the cost value for the two organs at risk (OARs) was decreased by 60% and 92%. Our study of the proposed novel DIM-PADM-based RDAO algorithm makes two main contributions: First, we validate the use of the proposed algorithm, in contrast to the FMO–LSA framework, for direct optimization of aperture leaf positions and show that this method results in more precise dose conformality. Second, we demonstrate that compared to MC, the DIM-PADM-based method significantly reduces the computational time required for DAO.
Highlights
Intensity modulated radiation therapy (IMRT) [1,2,3,4] can produce a high degree of dose conformality directed at tumor targets while sparing the organs at risk (OARs)
direct aperture optimization (DAO) can be modeled on -Monte Carlo (MC) [21] dose calculation; an approximation of MC, such as the pencil beam model; or dose influence matrix (DIM)-based analytical models
We proved that the proposed DIM-PADMbased DAO method is a fast and accurate method for IMRT
Summary
Intensity modulated radiation therapy (IMRT) [1,2,3,4] can produce a high degree of dose conformality directed at tumor targets while sparing the organs at risk (OARs). Rapid direct aperture optimization via piecewise aperture dose model sequencing algorithm (LSA) [8,9,10]. Direct aperture optimization (DAO) [13] bypasses fluence intensity maps and directly solves for deliverable MLC apertures. In a study by Shepard et al [13], the time required for a C-shaped target with seven apertures was approximately 12 minutes when the MC-based DAO method was used. The column generation method models all possible apertures with linear combinations of DIM and iteratively updates the most likely aperture by solving a pricing problem. We utilize a DIM-based piecewise aperture dose model (PADM) for rapid dose calculation
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