167. Evaluation of a radiotherapy-dedicated Monte Carlo environment (PRIMO) for verification of clinical VMAT plans for brain and lung metastases

Abstract

PurposePRIMO is a graphical environment for MonteCarlo (MC) simulations. The Dose Planning Method (DPM) is a fast MC algorithm for the simulation of the deposited dose under radiotherapy conditions. The objective of this work was to validate the DPM-calculated beams against our LINAC EDGE and compare a clinical algorithm (Acuros, Varian) with PRIMO DPM MC in two different clinical scenarios. MethodsThe beams were evaluated in terms of profiles, PDDs, Output Factors (OF), Dosimetric Leaf Gap (DLG) and transmitted dose of the 120 HD MLC. PDDs were also evaluated in a slab-phantom with different materials. A set of 20 patients was selected for this study: 10 patients with brain metastases and 10 with lung metastases. For all patients VMAT plans with 10 MV FFF beam were optimized in Eclipse and calculated with Acuros. The DICOM files (plan, structure and images) were imported in PRIMO. DPM was used to calculate the dose distribution in the patients. The plans were compared in terms of DVHs through Homogeneity (HI) and Gradient (GI) Indexes. ResultsThe agreement between simulated and real beam was good with differences ⩽1.5% for all parameters considered. Some differences were observed in the MLC modeling. PRIMO showed a larger DLG with values ∼2 mm greater than both Acuros and the related experimental measurements (Fig. 1).The analysis of PDDs in the slab-phantom materials showed discrepancies of ∼1.2% between Acuros and PRIMO in cartilage and lung (Fig. 2). The MC dose distributions of the VMAT plans always had mean uncertainties within the PTV < 1.5%. Comparing the VMAT plans an overall good agreement was observed. ConclusionsPRIMO is an interesting tool for the clinical environment, useful to verify and support the commercially available TPS. The agreement with Acuros is good though further analysis should be done.