A Monte Carlo investigation of low‐Z target image quality generated in a linear accelerator using Varianˈs VirtuaLinaca). Issue 2 (23rd January 2014)

• Record Type: Journal Article
• Authors: Parsons, David; Robar, James L.; Sawkey, Daren
• Is Part Of: Medical physics. Volume 41:Issue 2(2014)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2014-01-23
• Subjects: Monte Carlo simulations -- Dosimetry/exposure assessment -- Contrast -- Therapeutic applications -- Applications -- Thermography; biomedical equipment -- biomedical optical imaging -- bone -- dosimetry -- linear accelerators -- medical image processing -- Monte Carlo methods -- phantoms -- radiation therapy; low‐Z target -- flattening filter free -- Monte Carlo; Radiation therapy -- Biological material, e.g. blood, urine; Haemocytometers -- Digital computing or data processing equipment or methods, specially adapted for specific applications -- Image data processing or generation, in general -- Linear accelerators -- Scintigraphy; Carbon -- Photons -- Medical imaging -- Linear accelerators -- Phase space methods -- Monte Carlo methods -- Medical image contrast -- Field size -- Phosphors -- Electron beams; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4861818
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: : The focus of this work was the demonstration and validation of VirtuaLinac with clinical photon beams and to investigate the implementation of low‐Z targets in a TrueBeam linear accelerator (Linac) using Monte Carlo modeling. Methods: : VirtuaLinac, a cloud based web application utilizing Geant4 Monte Carlo code, was used to model the Linac treatment head components. Particles were propagated through the lower portion of the treatment head using BEAMnrc. Dose distributions and spectral distributions were calculated using DOSXYZnrc and BEAMdp, respectively. For validation, 6 MV flattened and flattening filter free (FFF) photon beams were generated and compared to measurement for square fields, 10 and 40 cm wide and at dmax for diagonal profiles. Two low‐Z targets were investigated: a 2.35 MeV carbon target and the proposed 2.50 MeV commercial imaging target for the TrueBeam platform. A 2.35 MeV carbon target was also simulated in a 2100EX Clinac using BEAMnrc. Contrast simulations were made by scoring the dose in the phosphor layer of an IDU20 aSi detector after propagating through a 4 or 20 cm thick phantom composed of water and ICRP bone. Results: : Measured and modeled depth dose curves for 6 MV flattened and FFF beams agree within 1% for 98.3% of points at depths greater than 0.85 cm. Ninety three percent or greater of points analyzed for the diagonal profiles had a gamma value less than one for the criteria of 1.5 mm and 1.5%. The two low‐Z target photon spectra produced in TrueBeam are harder than that from the carbon target in the Clinac. Percent dose at depth 10 cm is greater by 3.6% and 8.9%; the fraction of photons in the diagnostic energy range (25–150 keV) is lower by 10% and 28%; and contrasts are lower by factors of 1.1 and 1.4 (4 cm thick phantom) and 1.03 and 1.4 (20 cm thick phantom), for the TrueBeam 2.35 MV/carbon and commercial imaging beams, respectively. Conclusions: : VirtuaLinac is a promising new tool for Monte Carlo modeling of novel target designs. A significant spectral difference is observed between the low‐Z target beam on the Clinac platform and the proposed imaging beam line on TrueBeam, with the former providing greater diagnostic energy content.