OBJECTIVE To evaluate the performance of RapidArc® (Eclipse 10.0.28) and SmartArc® (Pinnacle 9.0) radiotherapy plans for lung stereotactic body radiation therapy (SBRT) in terms of dosimetric plan quality, delivery efficiency, inhomogeneity corrections and accuracy of dose delivery using a custom-built heterogeneity insert for ArcCHECK™ (Sun Nuclear Corp., FL, USA). METHODS SmartArc® and RapidArc® plans were generated for 10 patients. The quality of the plans was evaluated in terms of conformity indices (R100 and R50 ) and the dose to the organs at risk. The efficiency was evaluated in terms of the monitor units (MUs) required for a given prescription dose. For dose verification, we designed and manufactured a heterogeneity insert for ArcCHECK™ with densities that simulate soft tissue, lung, bone, and air and having multiple locations for point dose measurements. Accuracy of dose delivery was assessed using gamma analysis. RESULTS The overall plan quality was similar when comparing SmartArc® with RapidArc®. However, RapidArc® plans required significantly more MUs-up to 72%™compared with SmartArc® plans (p<0.001). ArcCHECK™ measurements in the presence of inhomogeneities showed better agreement for SmartArc® plans. CONCLUSIONS Plan quality for SmartArc® and RapidArc® was comparable. However, SmartArc® plans were more efficient, requiring significantly fewer monitor units, and were delivered more accurately in a non-homogeneous phantom. With the custom-built heterogeneity insert, ArcCHECK™ can be used efficiently to verify inhomogeneity corrections and dose delivery accuracy for lung SBRT plans.