ABSTRACT
Objective To investigate the feasibility of sequential intensity-modulated radiotherapy (sIMRT)and simultaneously integrated boost intensity-modulated radiotherapy(SIB-IMRT)in the radiotherapy of brain metastasis,the dosimetric difference of target volumes and organs at risk(OARs). Methods Twenty pa-tients diagnosed as brain metastasis were randomly selected,with SIB-IMRT and sIMRT programs developed for each patient. Dosimetric differences between target areas and OARs were compared between the two radiotherapy protocols. Results Compared with sIMRT,SIB-IMRT had no significant difference in the average irradiation dose of the brainstem[(42.69 ± 2.18)Gy vs.(41.98 ± 0.96)Gy]and homogeneity index(HI)(1.46 ± 0.04 vs.1.42 ± 0.13)of P-CTV(P > 0.05). However,SIB-IMRT plan achieved higher than sIMRT in the conformation index (CI)(0.68 ± 0.05 vs. 0.44 ± 0.04)and HI(1.03 ± 0.01 vs. 1.06 ± 0.01)of P-GTV. Meanwhile,both maximum exposure dose of OARs and CI of P-CTV(0.68 ± 0.05 vs.0.44 ± 0.04)of SIB-IMRT were significant in comparison with sIMRT(P<0.05).Conclusions Both radiotherapies can meet target coverage and dose requirements.Com-pared to sIMRT technique,SIB-IMRT technique can decrease effectively the exposure dose of surrounding organs, and can give the tumor target more uniform physical dose conformation.
ABSTRACT
Objective To explore the dosimetry of simplified intensity modulated radiotherapy (sIMRT)in the spinal component of craniospinal irradiation(CSI)compared with conventional plan(3D-CRT).Methods Five previously treated patients were adopted to generate 3D-CRT,3-and 5-field slMRT plans.The prescribed dose was 36 Gy to the planning target volume(PTV)in 20 fractions.The dose distributions of target volume and normal tissues,and homogeneity index(HI)were ananlyzed using the dose volume histogram.The total monitor units(MUs)were also analyzed to compare the delivery time indirectly.Results For 3D-CRT plans,the region of the neighbouring fields only received 70％ of the prescribed dose,and the maximum dose delivered in the normal tissues was increased to approximately 140％ of the prescribed dose.The homogeneity index(HI)of 3-and 5-field sIMRT were 0.09 ± 0.01 and 0.08 ±0.01,respectively,superior to that of 3D-CRT(0.18 ± 0.02,t=7.80,7.65,P＜0.05).The values of V10 for the heart of 3-and 5-field sIMRT were(8.4 ± 1.9)％ and(8.4 ± 2.0)％,respectively,lower than that of 3D-CRT((36.0 ± 6.0)％(t=13.3,13.0,P＜0.05).V20 for the thyroid gland were (12.4±1.5)％ and(12.4±1.6)％,respectively,lower than(69.4±5.7)％ of 3D-CRT(t=26.3,26.4,P＜0.05).V20 for the larynx were(17.2 ± 1.2)％ and(17.9 ± 1.5)％,respectively,lower than that of 3D-CRT[(89.4±7.0)％(t=25.5,26.5,P＜0.05)].V30for the NTwas(4.4±1.4)％,(4.9± 1.9)％,lower than that of 3 D-CRT[(31.9 ± 6.1)％(t=8.5,10.1,P＜0.05)].The averaged values of total MUs for 3-and 5-field sIMRT were 1100 ± 177 and 1160 ±204,respectively,higher than that of 3D-CRT(640 ± 151).Conclusions Compared with the 3D-CRT CSI technique,3-and 5-field sIMRT have better dose distribution and can improve target dose uniformity and protect the organs at risk.