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• W4238972099 abstract "The purpose of this study is to examine the extent to which IMRT planning and delivery can be simplified through the use of Direct Aperture Optimization (DAO). The key feature of DAO is that it optimizes the segment shapes and weights directly rather than optimizing the intensity patterns. All of the constraints imposed by the multileaf collimator are directly incorporated into the IMRT optimization. DAO allows the user to specify the number of apertures per beam angle in the prescription. The DAO algorithm is then able to find the optimal treatment plan for that number of apertures. The user is thus provided with control of the complexity of the plan delivery. Prior to clinical implementation, the DAO algorithm was benchmarked through a systematic study of the degree to which IMRT treatment plans can be simplified (using a small number of apertures) without sacrificing the dosimetric quality of the plans. For three patient cases, IMRT plans were first generated with two commercial inverse planning systems (Pinnacle and CORVUS). A series of optimizations were then performed with DAO. Each optimization used identical beam angles and optimization constraints. The only variable that was changed from one optimization to the next was the number of apertures per beam direction. The optimized treatment plans were analyzed through comparisons of the resulting objective function values and the corresponding DVHs. Thereby we obtain 1) the minimum number of apertures required by DAO to produce a plan with comparable dose conformity with beamlet-based treatment planning systems; and 2) the asymptotic limits of the number of apertures required for different sites when using DAO. After the benchmarking was complete, DAO was implemented clinically at the University of Maryland School of Medicine using the Prowess treatment planning system. Initial treatment sites include head-and-neck, prostate, and pancreas. For each patient, the pencil beam and final dose calculation are performed using a convolution/superposition based dose engine, and the treatments are delivered on an Elekta SL20 linear accelerators. The results indicate that the required number of apertures per beam direction is dependant upon the complexity of the case. For simple cases with a convex tumor volume and a separation between the tumor and the organs at risk, there is little improvement in the objective function and the corresponding DVHs beyond three apertures per beam direction. However, for large and complex tumor volumes, the objective function and its DVHs are converge more slowly as the number of apertures is increased. This is particularly true if the target is concave in nature or if the treatment seeks to simultaneously treat multiple target volumes. For these most complex cases, it has been observed that nine or more apertures per beam angle are often necessary to achieve an IMRT treatment plan of the highest quality. Overall, the benchmarking study revealed that for the majority of IMRT patient cases, there is little dosimetric gain in increasing the number of apertures per beam angle beyond six. In comparison with beamlet-based inverse planning systems, the number of segments was reduced between 50 and 90 percent. Initial clinical results are consistent with the benchmarking studies. For all cases, between 21 and 45 apertures have been used for the optimized treatment plan. This allows the patients to be treated in a traditional fifteen minute time slot. Consequently, there are few if any negative consequences in terms of patient throughput as compared with 3D conformal treatments. Pre-clinical benchmark studies along with clinical patient deliveries at the University of Maryland have demonstrated that Direct Aperture Optimization produces highly conformal IMRT treatment plans comparable to beamlet-based IMRT while using a small number of apertures per beam angle. DAO addresses many of the issues associated with the increased complexity of IMRT treatment plans including reduced patient throughput, increased staffing requirements, and additional wear-and-tear on treatment machines" @default.
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• W4238972099 date "2004-09-01" @default.
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• W4238972099 title "Simplifying planning and delivery of IMRT using direct aperture optimization" @default.
• W4238972099 doi "https://doi.org/10.1016/s0360-3016(04)01163-0" @default.
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