document: Incorporating multi-leaf collimator leaf sequencing into iterative IMRT optimization Intensity modulated radiation therapy -LRB- IMRT -RRB- treatment planning typically considers beam optimization and beam delivery as separate tasks . Following optimization , a multi-leaf collimator -LRB- MLC -RRB- or other beam delivery device is used to generate fluence patterns for patient treatment delivery . Due to limitations and characteristics of the MLC , the deliverable intensity distributions often differ from those produced by the optimizer , leading to differences between the delivered and the optimized doses . Objective function parameters are then adjusted empirically , and the plan is reoptimized to achieve a desired deliverable dose distribution . The resulting plan , though usually acceptable , may not be the best achievable . A method has been developed to incorporate the MLC restrictions into the optimization process . Our in-house IMRT system has been modified to include the calculation of the deliverable intensity into the optimizer . In this process , prior to dose calculation , the MLC leaf sequencer is used to convert intensities to dynamic MLC sequences , from which the deliverable intensities are then determined . All other optimization steps remain the same . To evaluate the effectiveness of deliverable-based optimization , 17 patient cases have been studied . Compared with standard optimization plus conversion to deliverable beams , deliverable-based optimization results show improved isodose coverage and a reduced dose to critical structures . Deliverable-based optimization results are close to the original nondeliverable optimization results , suggesting that IMRT can overcome the MLC limitations by adjusting individual beamlets . The use of deliverable-based optimization may reduce the need for empirical adjustment of objective function parameters and reoptimization of a plan to achieve desired results
doc_bio_tags: O B I I I O O O O B I I I O O O B I O O B I O B I O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I I O O O O O O O O O
extractive_keyphrases: intensity modulated radiation therapy treatment planning multileaf collimator leaf sequencing beam delivery beam optimization fluence patterns objective function parameters deliverable dose distribution empirical adjustment
abstractive_keyphrases: iterative optimization tumor dose optimized intensity gradient-based search algorithm beamlet ray intensities newton method dose-volume objective values