Vijayan Sarath, Xiong Zhenyu, Guo Chao, Troville Jonathan, Islam Naveed, Rudin Stephen, Bednarek Daniel R
Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA.
Department of Radiology, University at Buffalo, Buffalo, NY, USA.
Proc SPIE Int Soc Opt Eng. 2018 Feb;10573. doi: 10.1117/12.2294920. Epub 2018 Mar 9.
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 EGS Monte-Carlo and Gafchromic film as a function of x-ray field size and beam penetrability. Forward scatter point spread function's (PSF) were generated with EGS 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 PSF 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 PSF'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 forward-scatter 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.
研究了透视介入过程中患者检查床产生的前向散射剂量分布及其对皮肤剂量的贡献。使用EGS蒙特卡罗方法和Gafchromic胶片，计算了与水等效体模和患者检查床产生的皮肤前向散射剂量分布，作为X射线野大小和射线穿透性的函数。利用EGS从入射到水模和患者检查床上的1×1 mm模拟初级铅笔束生成前向散射点扩散函数（PSF）。将归一化到初级的前向散射点扩散函数与初级剂量分布进行卷积，以生成散射剂量分布。研究了PSF使用DTS（剂量跟踪系统）软件计算入射皮肤剂量分布的效用。针对5×5 cm、9×9 cm、13.5×13.5 cm大小的X射线野的水模，以及针对16.5×16.5 cm野的患者检查床，分别对2.32 mm、3.10 mm、3.84 mm和4.24 mm铝半值层X射线束进行了前向散射分布计算。通过散射剂量PSF的卷积，利用DTS确定皮肤剂量，并在PMMA“患者模拟”块下使用Gafchromic胶片确定均匀和成形X射线野的皮肤剂量。使用卷积方法为与水等效体模确定的归一化前向散射分布与使用EGSnrc为全场计算的结果在±6%范围内一致。针对16.5×16.5 cm视野为患者检查床计算的归一化前向散射剂量分布与使用胶片确定的结果在±2.4%范围内一致。对于均匀的PMMA体模，无论是均匀还是非均匀X射线野，使用DTS计算的皮肤剂量与使用胶片测量的结果在±2%范围内。与在整个野上使用单个前向散射值相比，卷积方法提供了更高的精度，并且是执行全场蒙特卡罗计算的更快替代方法。
