Organ at risks sparing with simultaneous integrated boost volumetric modulated arc therapy for locally advanced non-small lung cancer: an automated treatment planning study

Abstract

Background : The technique of simultaneous integrated boost volumetric modulated arc therapy (SIB-VMAT) have been widely used in locally advanced non-small cell lung cancer, however, its dosimetric advantages are seldom reported. This study aimed to investigate the dosimetric benefit of SIB-VMAT compared to conventional VMAT plans (C-VMAT). Methods : Forty patients with stage III non-small cell lung cancer in our hospital were randomly selected for the two type prescriptions. SIB-VMAT and C-VMAT plans were generated for each patient with the same optimization parameter by the automatic treatment planning system (TPS). The prescribed dose was 50.4 Gy in 28 fractions to PTV and 59.92 Gy in 28 fractions to PGTV in SIB-VMAT plans, with 60 Gy in 30 fractions to PTV in C-VMAT plans. Dose-volume metrics for the planning target volume, lung, heart, esophagus and spinal cord were recorded. The quality score (S D ) was used to evaluate organ at risks (OARs) protection for two type prescription plans. Results : Conformal coverage of the PGTV/PTV by the 95% of the prescription dose was well achieved in automated plans. SIB-VMAT plans achieved significantly lower S D values than C-VMAT plans (Mean: 0.064±0.106 vs. 0.145±0.181, P=0.001). Obvious reductions in mean dose, V 30 , V 40 and V 50 of total lung were observed in SIB-VMAT plans compared to C-VMAT plans, with median decreased proportions of 6.5%、8.7%、19.6% and 32.1%. Statistically significant decrease in heart V 30 and V 40 were also achieved in SIB-VMAT plans, with median decreased proportions of 26.1% and 38.8%. SIB-VMAT plans achieved significant reductions in the maximum doses to both esophagus and spinal cord. Conclusions : SIB-VMAT technique could lead to a substantial sparing of normal organs, including lung, heart, esophagus and cord, mainly through reducing high and inter-median dose exposure.