Calculation of the entrance skin dose distribution for fluoroscopically guided interventions using a pencil beam backscatter model

Sarath Vijayan; Zhenyu Xiong; Stephen Rudin; Daniel R. Bednarek

doi:10.1117/1.JMI.4.3.031203

14 June 2017 Calculation of the entrance skin dose distribution for fluoroscopically guided interventions using a pencil beam backscatter model

Sarath Vijayan, Zhenyu Xiong, Stephen Rudin, Daniel R. Bednarek

Author Affiliations +

Journal of Medical Imaging, Vol. 4, Issue 3, 031203 (June 2017). https://doi.org/10.1117/1.JMI.4.3.031203

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.

Citation Download Citation

Sarath Vijayan, Zhenyu Xiong, Stephen Rudin, and 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

Received: 19 December 2016; Accepted: 31 May 2017; Published: 14 June 2017

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