Dosimetric study of different intensity-modulated modalities in the radiotherapy for mid and upper thoracic esophageal carcinoma

Abstract

Objective To compare the static intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for mid and upper thoracic esophageal cancer.Method The data of twenty esophageal cancer patients were retrospectively re-planned with VMAT(single arc and double arcs) modality using Pinnacle treatment plan system.Five of these patients were selected again to simulate single arc plans with different segment intervals (4°,3°,2°) and re-planned on other treatment planning systems (Monaco and MasterPlan).Differences of dose distribution and treatment parameters were compared.Results In comparison to IMRT and single-VMAT (S-VMAT),Double-VMAT (D-VMAT) significantly improves the dosimetric parameters for targets(P ＜ 0.05),dose homogeneity(P ＜ 0.05) and conformity(P ＜ 0.05).Though VMAT plans were slightly better than IMRT in reducing the doses to the organs at risk (OARs),no advantage was observed in the low-dose protection of lung and E-P (P ＜ 0.05).For the VMAT plans with different segment intervals,lower OAR doses were observed using an interval of 2°(P ＜ 0.05),except for the mean dose of the heart.For the VMAT plans on different treatment planning systems,Monaco-based plans protected OARs better (P ＜ 0.05).The number of monitor units (MU) and treatment time were less in VMAT cases.Conclusions VMAT plans perform better in target coverage,dose homogeneity and conformity,and can reduce the radiation dose to the spinal cord,lungs,heart and other normal tissue than IMRT plans.The VMAT plan quality could be further improved by using double arcs and smaller segment interval.Monaco-based plans provide better OAR protections under the same conditions of physical and optimization parameters. Key words: Intensity-modulated radiotherapy; Volumetric modulated arc therapy; Esophageal cancer ; Dosimetry