RESUMO
Objective To study the dosimetric impact of different angle fields in intensitymodulated radiotherapy (IMRT) and the feasibility of beam angle optimization (BAO) for multiple intracranial metastases.Methods In total,11 patients with multiple intracranial metastases were included in these analyses.Two treatment techniques were designed for each patient:the 7 equal spaced fields (BAF group) IMRT,and 7 fields by beam angle optimization (BAO group) IMRT.The dose distribution in the target,the dose to the organs at risk and normal brain tissues,and total MU in two groups were compared to explore the dosimetric differences.Results In comparison to the BAF group,the BAO group reduced the maximum dose to left and right lenses by an average of 45％,37％ (t =-5.707,-4.438,P ＜ 0.05);the mean dose to the left and right eyes were reduced by an average of 42.6％,44.5％ (t =-4.380,-5.638,P ＜0.05);the maximum dose to the right eyes were reduced by an average of 32.5％ (t =-2.518,P ＜ 0.05).The maximum dose of the right optic nerve and the mean dose of normal brain tissue were reduced by an average of 23％ and 3％ (t =-3.105,-3.437,P ＜0.05),respectively.For the target dose,conformity and homogeneity in PTV,no statistical differences were observed between the two groups (P ＞ 0.05).The BAO group reduced the maximum dose of the brainstem and the optic chiasm,as well as the number of MU,however,the differences were not statistically significant (P ＞ 0.05).Conclusions In comparison to the BAF group,the BAO group shows a similar target dose and reduces the dose for the organs at risk.For multiple intracranial metastases,IMRT protocols with BAO are feasible and beneficial.
RESUMO
Objective To evaluate the performace of fixed field Intensity modulated radiation therapy (IMRT) and RapidArc in the radiotherapy for multiple intracranial metastases.Methods The clinical data of 10 patients with multiple intracranial metastases,8 male and 2 female,aged 65-73,were used to design 3 plans:fixed field IMRT,RapidArc with single Arc (RA1),and RapidArc with double Arc (Arc 2).Dose-volume-histogram analysis was used to compare dose results,monitor unit,and delivery time.Results All 3 plans met the clinical requirements.The best target conformity and homogeneity were observed in the RA2 plan (Z = -2.803,- 2.904,P ＜ 0.05) and there were no statistical differences between the IMRT plan and RA1 plan.The maximum doses to the lens,eyes,and brainstem of the two RapidArc plans were all significantly lower than those of the IMRT plan(Z = -2.803--2.191 ,P ＜0.05),and the maximum dose to the optic nerves of the RA2 plan was significantly lower than that of the IMRT plan (Z = -2.293,-2.701 ,P ＜0.05).Compared with the IMRT plan,the average monitor units of the RA1 and RA2 plans were reduced by 29% and 24%,respectively,and the delivery time of these plans were significantly shorter by 84% and 69%,respectively.Conclusions Compared to the IMRT plan,RapidArc plans with single or double Arcs show similar or better effects in the target dose distribution,reduction of irradiation doses on organs at risk and,moreover,significant decrease of the monitor units and delivery time.