Configuration of volumetric arc radiotherapy simulations using PRIMO software: A feasibility study

Abstract

Volumetric Modulated Arc Therapy (VMAT) uses non-uniform intensity fields allowing volumetric complex dose distributions. The simultaneous MultiLeaf Collimator (MLC) motion and Gantry rotation pose difficulties in the dose distribution calculation by Treatment Planning Systems (TPS). Furthermore, a dedicated Quality Assurance (QA) program and patient-specific dose verifications are requested. Monte Carlo dose calculation in Radiotherapy (RT) is a gold standard due to its most detailed description of radiation-matter interaction. Recently, the PRIMO software was proposed, providing several built-in RT units models, including TrueBeam. Nevertheless, VMAT is not implemented yet. In this work, TrueBeam was simulated in PRIMO using 6 and 10 MV in Flatness Filter Free (FFF) mode and at 15 MV with Flatness Filter inserted. The results were validated by Gamma Function (2%, 2 mm) based on reference measurements in water tank. The VMAT complex dynamic delivery is divided into a customizable number of probabilistically sampled static configurations of jaws, leaves and gantry angles. In-house algorithms were developed to interpolate the LINAC geometrical information along the process once the planned information is retrieved from the TPS output DICOM file. A Graphical User Interface (GUI) was developed to assist the user to configure PRIMO to simulate complex deliveries. Static simulations in reference conditions showed always >97% of Gamma points <1 for PDD and profiles at various depths and fields sizes for the 6, 10 and 15 MV primary beam respectively. The GUI properly read, manipulated and wrote the configuration data in a “ppj” format, which was accepted by PRIMO. The dynamic jaws, MLC and gantry motion were positively assessed by visual inspection of the static beam configuration in PRIMO. Dynamic irradiations were simulated and the gamma function tests against reference dose distributions showed good agreement with typical QA criteria. A GUI to configure PRIMO for VMAT irradiations allowed to enable a flexible workflow for simulating a general dynamic treatment.