Skin dose mapping for non-uniform x-ray fields using a backscatter point spread function

Beam shaping devices like ROI attenuators and compensation filters modulate the intensity distribution of the xray beam incident on the patient. This results in a spatial variation of skin dose due to the variation of primary radiation and also a variation in backscattered radiation from the patient. To determine the backscatter component, backscatter point spread functions (PSF) are generated using EGS Monte-Carlo software. For this study, PSF’s were determined by simulating a 1 mm beam incident on the lateral surface of an anthropomorphic head phantom and a 20 cm thick PMMA block phantom. The backscatter PSF’s for the head phantom and PMMA phantom are curve fit with a Lorentzian function after being normalized to the primary dose intensity (PSFn). PSFn is convolved with the primary dose distribution to generate the scatter dose distribution, which is added to the primary to obtain the total dose distribution. The backscatter convolution technique is incorporated in the dose tracking system (DTS), which tracks skin dose during fluoroscopic procedures and provides a color map of the dose distribution on a 3D patient graphic model. A convolution technique is developed for the backscatter dose determination for the nonuniformly spaced graphic-model surface vertices. A Gafchromic film validation was performed for shaped x-ray beams generated with an ROI attenuator and with two compensation filters inserted into the field. The total dose distribution calculated by the backscatter convolution technique closely agreed with that measured with the film.

[1]  Iwan Kawrakow,et al.  The EGSnrc System, a Status Report , 2001 .

[2]  Daniel R. Bednarek,et al.  MO-F-CAMPUS-I-01: A System for Automatically Calculating Organ and Effective Dose for Fluoroscopically-Guided Procedures , 2015 .

[3]  Stephen Balter,et al.  Fluoroscopically guided interventional procedures: a review of radiation effects on patients' skin and hair. , 2010, Radiology.

[4]  T Mather,et al.  Area x-ray beam equalization for digital angiography. , 1999, Medical physics.

[5]  N Petoussi-Henss,et al.  Calculation of backscatter factors for diagnostic radiology using Monte Carlo methods. , 1998, Physics in medicine and biology.

[6]  S Rudin,et al.  Clinical application of region-of-interest techniques to radiologic imaging. , 1996, Radiographics : a review publication of the Radiological Society of North America, Inc.

[7]  S Rudin,et al.  Region of interest fluoroscopy. , 1992, Medical physics.

[8]  Daniel R. Bednarek,et al.  TH‐AB‐201‐01: A Real‐Time Skin‐Dose Mapping System for Region‐Of‐Interest (ROI) Fluoroscopy , 2015 .

[9]  Stephen Rudin,et al.  Organ and effective dose reduction for region-of-interest (ROI) CBCT and fluoroscopy , 2017, Medical Imaging.

[10]  Stephen Rudin,et al.  Incorporating corrections for the head-holder and compensation filter when calculating skin dose during fluoroscopically guided interventions , 2015, Medical Imaging.

[11]  Stephen Rudin,et al.  Verification of the performance accuracy of a real-time skin-dose tracking system for interventional fluoroscopic procedures , 2011, Medical Imaging.

[12]  S Rudin,et al.  A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system. , 2016, Medical physics.

[13]  James C. L. Chow,et al.  Surface dose reduction from bone interface in kilovoltage X‐ray radiation therapy: a Monte Carlo study of photon spectra , 2012, Journal of applied clinical medical physics.

[14]  Daniel R. Bednarek,et al.  A system to track skin dose for neuro-interventional cone-beam computed tomography (CBCT) , 2016, SPIE Medical Imaging.

[15]  Tomas Akenine-Möller,et al.  Fast, minimum storage ray/triangle intersection , 1997, J. Graphics, GPU, & Game Tools.

[16]  Hugo Bouchard,et al.  Backscatter factors and mass energy-absorption coefficient ratios for diagnostic radiology dosimetry , 2011, Physics in medicine and biology.

[17]  Stephen Rudin,et al.  Lens of the eye dose calculation for neuro-interventional procedures and CBCT scans of the head , 2016, SPIE Medical Imaging.

[18]  Daniel R. Bednarek,et al.  Integration of kerma-area product and cumulative air kerma determination into a skin dose tracking system for fluoroscopic imaging procedures , 2016, SPIE Medical Imaging.

[19]  Stephen Rudin,et al.  Monte Carlo investigation of backscatter point spread function for x-ray imaging examinations , 2017, Medical Imaging.

[20]  S Rudin,et al.  TU-D-209-02: A Backscatter Point Spread Function for Entrance Skin Dose Determination. , 2016, Medical physics.

[21]  C. Martin.  Measurement of patient entrance surface dose rates for fluoroscopic x-ray units. , 1995, Physics in medicine and biology.

[22]  Jan Seuntjens,et al.  Characterization of calibration curves and energy dependence GafChromic™ XR-QA2 model based radiochromic film dosimetry system. , 2014, Medical physics.