A Monte Carlo calculation model of electronic portal imaging device for transit dosimetry through heterogeneous media. Issue 5 (6th April 2016)

• Record Type: Journal Article
• Authors: Yoon, Jihyung; Jung, Jae Won; Kim, Jong Oh; Yeo, Inhwan
• Is Part Of: Medical physics. Volume 43:Issue 5(2016)
• Page Start: 2242
• Page End: 2250
• Publication Date: 2016-04-06
• Subjects: biomedical imaging -- calibration -- dosimetry -- ionisation chambers -- Monte Carlo methods -- phantoms -- radiation therapy; Dose‐volume analysis -- Therapeutic applications, including brachytherapy -- Monte Carlo methods -- Standards and calibration -- Dosimetry/exposure assessment; Radiation therapy -- Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00 -- Biological material, e.g. blood, urine; Haemocytometers -- Calibrating of instruments or apparatus -- Scintigraphy; transit dosimetry -- Monte Carlo -- EPID -- heterogeneous media -- XVMC; Image guided radiation therapy -- Phase space methods -- Field size -- Medical imaging -- Dosimetry -- Monte Carlo methods -- Calibration -- Lungs -- Computer modeling -- Photons; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4945276
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: To develop and evaluate a fast Monte Carlo (MC) dose calculation model of electronic portal imaging device (EPID) based on its effective atomic number modeling in the XVMC code. Methods: A previously developed EPID model, based on the XVMC code by density scaling of EPID structures, was modified by additionally considering effective atomic number ( Z eff ) of each structure and adopting a phase space file from the EGSnrc code. The model was tested under various homogeneous and heterogeneous phantoms and field sizes by comparing the calculations in the model with measurements in EPID. In order to better evaluate the model, the performance of the XVMC code was separately tested by comparing calculated dose to water with ion chamber (IC) array measurement in the plane of EPID. Results: In the EPID plane, calculated dose to water by the code showed agreement with IC measurements within 1.8%. The difference was averaged across the in‐field regions of the acquired profiles for all field sizes and phantoms. The maximum point difference was 2.8%, affected by proximity of the maximum points to penumbra and MC noise. The EPID model showed agreement with measured EPID images within 1.3%. The maximum point difference was 1.9%. The difference dropped from the higher value of the code by employing the calibration that is dependent on field sizes and thicknesses for the conversion of calculated images to measured images. Thanks to the Z eff correction, the EPID model showed a linear trend of the calibration factors unlike those of the density‐only‐scaled model. The phase space file from the EGSnrc code sharpened penumbra profiles significantly, improving agreement of calculated profiles with measured profiles. Conclusions: Demonstrating high accuracy, the EPID model with the associated calibration system may be used for in vivo dosimetry of radiation therapy. Through this study, a MC model of EPID has been developed, and their performance has been rigorously investigated for transit dosimetry.