A Monte Carlo model for independent dose verification in IMRT and VMAT for the Varian Novalis TX with high definition MLC

Purpose: With intensity modulated radiation therapy (IMRT), the physician can prescribe, design and deliver optimized treat-ment plans that target the tumor and spare adjacent critical structures. The increased conformity of such plans often comes at the expenses of adding significant complexity to the delivery of the treatment. With volumetrically modulated arc therapy (VMAT), in addition to the modulation of the intensity of the radiation beam, other mechanical parameters such as gantry speed and dose rate are varied during treatment delivery. It is therefore imperative that we develop comprehensive and accurate methods to validate such complex delivery techniques prior to the commencement of the patient’s treatment. Methods: In this study, a Monte Carlo simulation was performed for the high definition multileaf collimator (HD-MLC) of a Varian Novalis TX linac. Our simulation is based on the MCSIM code and provides a comprehensive model of the linac head. After validating the model in reference geometries, treatment plans for different anatomical sites were simulated and compared against the treatment plannin