Dosimetric Study Of Radiotherapy For Brain Metastasis

Objective: Sequential Intensity-Modulated Radiotherapy(s IMRT)and Simultaneously Integrated Boost Intensity-Modulated Radiotherapy(SIB-IMRT)were applied to the treatment of brain metastases.Two kinds of radiotherapy plans were designed for individual patient respectively,we aimed to study the feasibility of both methods in brain metastases and explore their dosimetric differences in targeted areas and organs at risk(OARs),then to provide the best radiotherapy plan for clinical treatment of brain metastases.Methods: Twenty pathologically confirmed brain metastasis patients were selected,and undergone body position fixation,computed tomograghy(CT)scanning,target delineation(including GTV,CTV and PTV)and OARs delineation(including bilateral crystals,brain stem,et al)with the TPS system.SIB-IMRT and s IMRT programs were developed for each individual.In the s IMRT plan,a dose of 40Gy/20 f was given to the whole brain target area(P-CTV),followed by a 20Gy/10 f intensity increment for the metastatic area(P-GTV),which made a total dose of 60Gy/30 f for the P-GTV.Meanwhile,the P-CTV and P-GTV were given a dose of 40Gy/24 f and 60Gy/24 f respectively in the SIB-IMRT plan.The dosimetric parameters of the target area and OARs of the two plans were recorded and processed with SPSS21.0.Dosimetric differences were assessed with paired t-test.Results: 1.Compared with s IMRT,SIB-IMRT achieved higher maximum dose of P-GTV and P-CTV,as well as greater average dose of P-GTV significantly(P<0.01).However,the minimum dose of P-GTV,the minimum and average dose of P-CTV in the SIB-IMRT plan were slightly lower than those in s IMRT(P>0.05).2.In terms of conformal index(CI),SIB-IMRT showed distinct advantages over s IMRT(P<0.01).The SIB-IMRT displayed better homogeneity index(HI)of P-GTV than s IMRT,whose difference was statistically significant(P<0.01).3.With regard to OARs,compared with s IMRT,the maximum and average dose of bilateral crystals and brain stem were lower in the SIB-IMRT plan,but there was no significant difference in the average exposure dose of brain stem(P=0.15).SIB-IMRT was significantly prior to s IMRT in maximum and average dose of bilateral crystals,together with the maximum dose of brain stem(P<0.01).Conclusions: 1.Both of the radiotherapies could meet the target area coverage and dosimetric requirements of brain metastases.2.Compared with s IMRT,SIB-IMRT achieved advanced CI and HI,particularly in the metastatic tumor area.3.In protecting OARs,SIB-IMRT could reduce more exposure dose of surrounding OARs than s IMRT,especially in the protection of bilateral crystals.