14 June 2017 Calculation of the entrance skin dose distribution for fluoroscopically guided interventions using a pencil beam backscatter model
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Abstract
Radiation backscattered from the patient can contribute substantially to skin dose in fluoroscopically guided interventions (FGIs). The distribution of backscatter is not spatially uniform, and use of a single backscatter factor cannot provide an accurate determination of skin dose. This study evaluates a method to determine the backscatter spatial distribution through convolution of a backscatter-to-primary (BP) point spread function (PSFn). The PSFn is derived for a pencil beam using EGSnrc Monte Carlo software and is convolved with primary distributions using a dose-tracking system. The backscatter distribution calculated using the convolution method is validated with Monte Carlo-derived distributions for three different size “uniform” fields and with XR-QA2 Gafchromic film for nonuniform x-ray fields obtained using region-of-interest (ROI) attenuators and compensation filters, both with homogenous poly-methyl methacrylate and nonhomogenous head phantoms. The BP ratios inside uniform fields were calculated within ± 2 % of that determined using EGSnrc. For shaped fields, the BP ratio in the unattenuated ROI was calculated within ± 3 % of that measured with film; in the beam-attenuated periphery, agreement was within ± 17 % , due to the larger uncertainty of the dose-response curve of the film in the low-dose region. This backscatter PSFn convolution method is much faster than performing full-field Monte Carlo calculations and provides improved accuracy in skin dose distribution determination for FGI procedures.
© 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
Sarath Vijayan, Sarath Vijayan, Zhenyu Xiong, Zhenyu Xiong, Stephen Rudin, Stephen Rudin, Daniel R. Bednarek, Daniel R. Bednarek, } "Calculation of the entrance skin dose distribution for fluoroscopically guided interventions using a pencil beam backscatter model," Journal of Medical Imaging 4(3), 031203 (14 June 2017). https://doi.org/10.1117/1.JMI.4.3.031203 . Submission: Received: 19 December 2016; Accepted: 31 May 2017
Received: 19 December 2016; Accepted: 31 May 2017; Published: 14 June 2017
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