ABSTRACT
Aiming at the disadvantages of traditional direct aperture optimization (DAO) method, such as slow convergence rate, prone to stagnation and weak global searching ability, a gradient-based direct aperture optimization (GDAO) is proposed. In this work, two different optimization methods are used to optimize the shapes and the weights of the apertures. Firstly, in order to improve the validity of the aperture shapes optimization of each search, the traditional simulated annealing (SA) algorithm is improved, the gradient is introduced to the algorithm. The shapes of the apertures are optimized by the gradient based SA method. At the same time, the constraints between the leaves of multileaf collimator (MLC) have been fully considered, the optimized aperture shapes are meeting the requirements of clinical radiation therapy. After that, the weights of the apertures are optimized by the limited-memory BFGS for bound-constrained (L-BFGS-B) algorithm, which is simple in calculation, fast in convergence rate, and suitable for solving large scale constrained optimization. Compared with the traditional SA algorithm, the time cost of this program decreased by 15.90%; the minimum dose for the planning target volume was improved by 0.29%, the highest dose for the planning target volume was reduced by 0.45%; the highest dose for the bladder and rectum, which are the organs at risk, decreased by 0.25% and 0.09%, respectively. The results of experiment show that the new algorithm can produce highly efficient treatment planning a short time and can be used in clinical practice.
ABSTRACT
Objective To compare the field-matching techniques and dosimetric characteristics in the target area of testicular seminoma including the abdominal and pelvic cavities between direct aperture optimization intensity modulated radiation therapy (DAO-IMRT) and 3D conformal radiation therapy (3D-CRT),and to analyse the advantages and disadvantages of DAO-IMRT.Methods DAO-IMRT and 3D-CRT plans were designed with Pinnacle treatment planning system for 7 testicular seminoma patients,and the characteristics of both the irradiation methods were analyzed and evaluated by means of the parameters like dose homogeneity indexes,dose volume histograms and etc.Results DAO-IMRT had the hot and cold volumes in the target areas both significantly smaller than those by 3D-CRT,while the conformity index and homogeneity index superior to those by 3D-CRT.The mean doses (Dmean) by DAO-IMRT of the organs at risk (OAR) except the left femur head were all lower than those by 3D-CRT,aud the V15 values of liver,double kidney,small intestine and rectum by DAO-IMRT were statistically lower than those by 3D-CRT (P＜0.01).3D-CRT had the V5 values of OAR all lower than those by DAO-IMRT,in which the differences of double kidney,small intestine,bladder,left femur head and normal tissues were significant statistically (P＜0.05).The monitor units by DAO-IMRT roughly doubled when compared with those by 3D-CRT,and the difference was also significant (P＜0.01).Conclusion DAO-IMRT with easy operation and high reliability can avoid the connection of fields in the target area of testicular seminoma,and is superior to 3D-CRT in dosimetry.