SU-F-T-641: Comparative Study On Planning and Delivery Efficiency of Volumetric Modulated Arc Therapy Between Varian and Elekta Platforms for SBRT Lung Treatment.

PURPOSE: To compare the plan quality between Eclipse (Varian) and Monaco (Elekta) TPS. To ascertain, if SBRT lung treatment could be delivered in a single coplanar arc (360 degrees) with both Elekta and Varian platforms. To assess if the smaller leaf width in Varian Millennium and Elekta Agility MLC heads have a dosimetric advantage over Elekta MLCi2 head METHODS: Ten SBRT lung patients (PTV volumes ranging from 11 cc to 103cc) who were previously treated on Varian Linac with non-coplanar arcs and received 50Gy in 5 fractions were chosen for this study. The patients were replanned in Eclipse TPS (AAA algorithm) using a 360 degree coplanar single arc (SA) delivery technique and 2 partial complimentary 180 degree arcs (PA). Treatment planning using single coplanar arc (360 degree arc) was also done on Monaco TPS (Montecarlo) for both Agility (160 leaf) and MLCi2 (80 leaf) Elekta MLC heads RESULTS: The average monitor units to deliver 10 Gy across all delivery methods were 3000 ± 474 MU and did not vary with PTV size. Coplanar single arc and partial arc techniques did not compromise either the RTOG 0813 or 0915 low dose spillage criteria for R50% or the maximum dose to any point 2cm away from the PTV. OAR doses to spinal cord, heart, great vessels, esophagus, rib and lung were comparable on both Eclipse (Varian) and Monaco (Elekta) platforms regardless of the delivery method.

CONCLUSION: SBRT lung tumors can be treated with a single coplanar 360 degree arc in both Varian and Elekta platforms. Non coplanar arcs and increasing arc degrees more than 360 degrees had no benefit in this study regardless of the volume of PTV. 0.5 cm leaf width used in Millennium and Agility MLC heads had no significant dosimetric improvement over 1 cm leaves in the MLCi2 head.