Year

2013

Degree Name

Master of Science - Research

Department

Department of Engineering

Abstract

In this study, a simple method of performing treatment dose verification for Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) using an Electronic Portal Imaging Device (EPID) was investigated. This work was based on a model for IMRT verification using Varian EPIDs presented by Lee et al. (2009). The method presented by Lee et al. (2009) was modified and extended upon to include equipment from different vendors, different treatment planning systems, and to include verification of VMAT. The EPID dose verification QA system was designed and tested using an Elekta AxesseTM LINAC with an iViewGTTM EPID (Elekta AB, Sweden), and a Siemens Oncor ImpressionTM LINAC with an OptiVue 1000STTM EPID panel (Siemens Medical Solutions USA, Inc, USA).

The EPID dose verification system compared flood field (FF) corrected EPID images (calibrated to absolute dose) and dose fluences generated by a treatment planning system (TPS) at a pre-determined depth in water (dref). The depth in water was determined as the depth in water that had closest agreement to the dose response properties of the EPID. Methods to determine dref are described and validation of the dosimetry system have been made with Step and Shoot IMRT and dynamic VMAT fields for 6 and 10 MV beam energies. Two different planning systems were used for patient field generation for comparison with the measured EPID fluences, XiO® v4.64 and Monaco® v3.10 (Elekta AB, Stockholm, Sweden).

All measured IMRT and VMAT patient fields achieved greater than 95% agreement with the planning fluences (using 3 cGy / 3 mm gamma criteria) and were comparable to the pass-rates obtained by using the MapCHECK® two-dimensional diode array (Sun Nuclear Corporation, Florida, USA) as per current department procedure for IMRT dose verification. The dosimetry system developed using the EPID was found to be a suitable tool for use in clinical pre-treatment dose verification and has since been implemented clinically.

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