A genetic algorithm used for the intensity level discretization in MLC leaf sequencing for step and shoot IMRT

A genetic algorithm used for the intensity level discretization in MLC leaf sequencing for step and shoot IMRT 1 2 first-author 2 3 2 corresp Corresponding author. E-mail address: bridgezbc@163.com, qhou@263.net Corresponding author. E-mail address: bridgezbc@163.com, qhou@263.net bridgezbc@163.com School of Physics Science and Technology , Sichuan University, Chengdu 610064, China School of Physics Science and Technology , Sichuan University, Chengdu 610064, China Key Laboratory of Radiation Physics and Technology, Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China Key Laboratory of Radiation Physics and Technology, Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China Department of Radiation Oncology, Huaxi Hospital, Sichuan University, Chengdu 610041, China Department of Radiation Oncology, Huaxi Hospital, Sichuan University, Chengdu 610041, China The inverse planning for a step-and-shoot plan in intensity-modulated radiotherapy (IMRT) is usually a multiple step process. Before being converted into the MLC segments, the optimum intensity profiles of beams, which are generated by an optimization algorithm, shall be discretized into a few intensity levels. The discretization process of the optimum intensity profiles can induce deviations in the final dose distribution from the original optimum dose distribution. This paper describes a genetic algorithm for the discretization of given optimum intensity profiles. The algorithm minimizes an objective function written in terms of the intensity levels. Both the dose-based objective function, which is defined by the deviation between the dose distributions before and after the discretization, and the intensity-based objective function, which is defined by the deviation between the optimum intensity profiles and the discretization intensity profiles, have been adopted. To evaluate this algorithm, a series of simulation calculations had been carried out using the present algorithm, the even-spaced discretization and the k -means clustering algorithm respectively. By comparing the resultant discretization-induced deviations (DIDs) in intensity profiles and in dose distributions, we have found that the genetic algorithm induced less DIDs in comparison with that induced in the even-spaced discretization or the k -means clustering algorithm. Additionally, it has been found that the DIDs created in the genetic algorithm correlate with the complexity of the intensity profiles that is measured by the "fluence map complexity" . IMRT Inverse planning Step-and-shoot Discretization References Bortfeld T R , Kahler D L , Waldron T J , et al . Oncol Biol Phys , 1994 , 28 : 723 - 730 . Oncol Biol Phys Chui C S , Chan M F , Yorke E , et al . Med Phys , 2001 , 28 : 2441 - 2449 . Med Phys Webb S . Intensity-modulated radiation therary , IOP Publishing Limited , 2001 . Intensity-modulated radiation therary Vaarkamp J , Adams E J , Warrington A P , et al . Radiother Oncol , 2004 , 73 : 65 - 72 . Radiother Oncol Galvin J , Chen X , Smith R . Int J Radiat Oncol Biol Phys , 1993 , 27 : 697 - 705 . Int J Radiat Oncol Biol Phys Siochi R A . Int J Radiat Oncol Biol Phys , 1999 , 43 : 671 - 680 . Int J Radiat Oncol Biol Phys Xia P , Verhey L J . Med Phys , 1998 , 25 : 1424 - 1434 . Med Phys Sun X , Xia P , Yu N . Med Phys , 2004 , 31 : 2402 - 2411 . Med Phys Keller R M A , Bortfeld T , Levegrun S , et al . Int J Radiat Oncol Biol Phys , 1999 , 45 : 1315 - 1324 . Int J Radiat Oncol Biol Phys Coolens C , Evans P M , Seco J , et al . Phys Med Biol , 2004 , 9 : 3857 - 3875 . Phys Med Biol Bar W , Alber M , Nusslin F . Phys Med Biol , 2001 , 46 : 1977 - 2007 . Phys Med Biol Beavis A W , Ganney P S , Whitton V J , et al . Phys Med Biol , 2001 , 46 : 2457 - 2465 . Phys Med Biol Wu Y , Yan D , Sharpe M B , et al . Med Phys , 2001 , 28 : 2188 - 2197 . Med Phys Nioutsikou E , Bedford J L , Christian J A , et al . Med. Phys , 2004 , 31 : 892 - 901 . Med. Phys Chen Y , Hou Q , Galvin J M . Med Phys , 2004 , 31 : 1504 - 1511 . Med Phys Hou Q , Wang J , Chen Y , et al . Med Phys , 2003 , 30 : 2360 - 2367 . Med Phys Low D A , Harms W B , Mutic S , et al . Med Phys , 1998 , 5 : 656 - 661 . Med Phys Boyer A , Mok E . Med Phys , 1985 , 12 : 169 - 177 . Med Phys Mackie T R , Scrimger J W , Battista J J . Med Phys , 1985 , 12 : 188 - 196 . Med Phys Llacer J , Deasy J O , Bortfeld T R , et al . Phys Med Biol , 2003 , 48 : 183 - 210 . Phys Med Biol Hou Q , Zhang C H , Wu Z W , et al . Med Phys , 2004 , 31 : 1339 - 1347 . Med Phys Hou Q , Wang J , Chen Y et al . Med Phys , 2003 , 30 : 61 - 68 . Med Phys Wu Q , Mohan R . Med Phys , 2002 , 29 : 1514 - 1527 . Med Phys Alber M , Meedt G , Nusslin F , et al . Med Phys , 2002 , 29 : 2584 - 2589 . Med Phys Alber M , Nusslin F . Phys Med Biol , 2000 , 45 : N49 - N52 . Phys Med Biol Spirou S V , Fournier B N , Yang J , et al . Med Phys , 2001 , 28 : 2105 - 2112 . Med Phys 10.1016/S1001-8042(08)60017-2 R817.5,O571.33 Supported by the National Natural Science Foundation of China (Grant No. 10275045) and the Excellent Young Teachers Program of China. 2006-05-28 2008-02-20 2021-01-19 2008 Nuclear Science and Techniques 01 19