Calculation of forward scatter dose distribution at the skin entrance from the patient table for fluoroscopically guided interventions using a pencil beam convolution kernel

Sarath Vijayan; Zhenyu Xiong; Chao Guo; Jonathan Troville; Naveed Islam; Stephen Rudin; Daniel R. Bednarek

doi:10.1117/12.2294920

9 March 2018 Calculation of forward scatter dose distribution at the skin entrance from the patient table for fluoroscopically guided interventions using a pencil beam convolution kernel

Sarath Vijayan, Zhenyu Xiong, Chao Guo, Jonathan Troville, Naveed Islam, Stephen Rudin, Daniel R. Bednarek

Author Affiliations +

Proceedings Volume 10573, Medical Imaging 2018: Physics of Medical Imaging; 1057363 (2018) https://doi.org/10.1117/12.2294920
Event: SPIE Medical Imaging, 2018, Houston, Texas, United States

Abstract

The forward-scatter dose distribution generated by the patient table during fluoroscopic interventions and its contribution to the skin dose is studied. The forward-scatter dose distribution to skin generated by a water table-equivalent phantom and the patient table are calculated using EGSnrc Monte-Carlo and Gafchromic film as a function of x-ray field size and beam penetrability. Forward scatter point spread function’s (PSFn) were generated with EGSnrc from a 1×1 mm simulated primary pencil beam incident on the water model and patient table. The forward-scatter point spread function normalized to the primary is convolved over the primary-dose distribution to generate scatter-dose distributions. The utility of PSFn to calculate the entrance skin dose distribution using DTS (dose tracking system) software is investigated. The forward-scatter distribution calculations were performed for 2.32 mm, 3.10 mm, 3.84 mm and 4.24 mm Al HVL x-ray beams for 5×5 cm, 9×9 cm, 13.5×13.5 cm sized x-ray fields for water and 3.1 mm Al HVL x-ray beam for 16.5×16.5 cm field for the patient table. The skin dose is determined with DTS by convolution of the scatter dose PSFn’s and with Gafchromic film under PMMA “patient-simulating” blocks for uniform and for shaped x-ray fields. The normalized forward-scatter distribution determined using the convolution method for water table-equivalent phantom agreed with that calculated for the full field using EGSnrc within ±6%. The normalized forwardscatter dose distribution calculated for the patient table for a 16.5×16.5 cm FOV, agreed with that determined using film within ±2.4%. For the homogenous PMMA phantom, the skin dose using DTS was calculated within ±2 % of that measured with the film for both uniform and non-uniform x-ray fields. The convolution method provides improved accuracy over using a single forward-scatter value over the entire field and is a faster alternative to performing full-field Monte-Carlo calculations.

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Sarath Vijayan, Zhenyu Xiong, Chao Guo, Jonathan Troville, Naveed Islam, Stephen Rudin, and Daniel R. Bednarek "Calculation of forward scatter dose distribution at the skin entrance from the patient table for fluoroscopically guided interventions using a pencil beam convolution kernel", Proc. SPIE 10573, Medical Imaging 2018: Physics of Medical Imaging, 1057363 (9 March 2018); https://doi.org/10.1117/12.2294920

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