The Effect of Collimator Angle on the Planned Dose of Dynamic Volumetric Modulated Arc Therapy in Patients with Locally Middle-Advanced Middle-Upper Esophageal Squamous Cell Carcinoma
Objective To explore the effect of different collimator angles on dose during dynamic volumetric modulated arc therapy(VMAT)in patients with locally middle-advanced middle-upper esophageal squamous cell carcinoma,and to provide reference for radiation therapy plan design.Methods With the selection of 18 patients with locally advanced esophageal squamous cell carcinoma who underwent VMAT in hospitals from January 2020 to August 2021 and other treatment parameters unchanged,the collimator angles were set to 0°,5°,10°,15°,20°,25°,30°,35°,40°,45°,and 50°,resulting in 11 plans.With the use of the collimator angle with 0 ° as a reference,the planning target volume(PTV)evaluation indicators[D98,D2,Dmean,homogeneity index(HI),conformity index(CI),and monitor unit(MU)]and organ at risk evaluation indicators[dual lung V5,V15,V20,heart V30,V40,spinal cord Dmax,and spinal cord planning risk(PRV)(obtained by spinal cord extension of 0.40 cm)Dmax]were compared for each plan.Results When the collimator angle was 15°,the HI and CI of the target area were both closest to 1,indicating that the uniformity and conformability of the target area were optimal at this time.When the collimator angle was 20 °,the HI of the target area changes significantly compared to° 0(t=2.406,P<0.05),and the V5 and V15 of both lungs changed significantly compared to 0 °(t=2.959,3.003,P<0.05).When the collimator angle increased to 45°,the number of MU significantly increased compared to 0°(t=-3.444,P<0.05).Conclusion When patients with locally advanced middle-upper stage esophageal squamous cell carcinoma receive VMAT,15°,as a relatively suitable collimator angle,can better protect the endangered organs while ensuring the dose distribution in the target area,and improve the treatment efficiency.
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