Assessment of Eye Lens Dose Reduction When Using Lateral Lead Shields on the Patient's Head during Neurointerventional Fluoroscopic Procedures and Cone-beam Computed Tomography (CBCT) Scans

The purpose of this study was to evaluate the effect of placing small lead shields on the temple region of the skull to reduce radiation dose to the lens of the eye during interventional fluoroscopically-guided procedures and cone-beam computed tomography (CBCT) scans of the head. EGSnrc Monte-Carlo code was used to determine the eye lens dose reduction when using lateral lead shields for single x-ray projections, CBCT scans with different protocols, and interventional neuroradiology procedures with the Zubal computational head phantom. A clinical C-Arm system was used to take radiographic projections and CBCT scans of anthropomorphic head phantoms without and with lead patches, and the images were compared to assess the effect of the shields. For single lateral projections, a 0.1 (0.3)-mm-thick lead patch reduced the dose to the left-eye lens by 40% to 60% (55% to 80%) from 45° to 90° RAO and to the right-eye lens by around 30% (55%) from 70° to 90° RAO. For different CBCT protocols, the reduction of lens dose with a 0.3-mm-thick lead patch ranged from 20% to 53% at 110 kVp. For CBCT scans of the anthropomorphic phantom, the lead patch introduced streak artifacts that were mainly in the orbital regions but were insignificant in the brain region where most neurointerventional activity occurs. The dose to the patient's eye lens can be reduced considerably by placing small lead shields over the temple region of the head without substantially compromising image quality in neuro-imaging procedures.

VirtualDose-IR: a cloud-based software for reporting organ doses in interventional radiology

A cloud-based software, VirtualDose-IR (Virtual Phantoms Inc., Albany, New York, USA), designed to report organ doses and effective doses for a diverse patient population from interventional radiology (IR) procedures has been developed and tested. This software is based on a comprehensive database of Monte Carlo-generated organ dose built with a set of 21 anatomically realistic patient phantoms. The patient types included in this database are both male and female people with different ages reflecting reference adults, obese people with different BMIs and pregnant women at different gestational stages. Selectable parameters such as patient type, tube voltage, filtration thickness, beam direction, field size, and irradiation site are also considered in VirtualDose-IR. The software has been implemented using the 'Software as a Service (SaaS)' delivery concept permitting simultaneous multi-user, multi-platform access without requiring local installation. The patient doses resulting from different target sites and patient populations were reported using the VirtualDose-IR system. The patient doses under different source to surface distances (SSD) and beam angles calculated by VirtualDose-IR and Monte Carlo simulations were compared. For most organs, the dose differences between VirtualDose-IR results and Monte Carlo results were less than 0.3 mGy at 15 000 mGy * cm2 kerma-area product (KAP). The organ dose results were compared with measurement data previously reported in literatures. The doses to organs that were located within the irradiation field match closely with experimental measurement data. The differences in the effective dose values between calculated using VirtualDose-IR and those measured were less than 2.5%. The dose errors of most organs between VirtualDose-IR and literature results were less than 40%. These results validate the accuracy of organ doses reported by VirtualDose-IR. With the inclusion of pre-specified clinical IR examination parameters (such as beam direction, target location, field of view and beam quality) and the latest anatomically realistic patient phantoms in Monte Carlo simulations, VirtualDose-IR provides users with accurate dose information in order to systematically compare, evaluate, and optimize IR plans.

Investigation of organ dose variation with adult head size and pediatric age for neuro-interventional projections

The purpose of this study was to evaluate the effect of patient head size on radiation dose to radiosensitive organs, such as the eye lens, brain and spinal cord in fluoroscopically guided neuro-interventional procedures and CBCT scans of the head. The Toshiba Infinix C-Arm System was modeled in BEAMnrc/EGSnrc Monte-Carlo code and patient organ and effective doses were calculated in DOSxynrc/EGSnrc for CBCT and interventional procedures. X-ray projections from different angles, CBCT scans, and neuro-interventional procedures were simulated on a computational head phantom for the range of head sizes in the adult population and for different pediatric ages. The difference of left-eye lens dose between the mean head size and the mean ± 1 standard deviation (SD) ranges from 20% to 300% for projection angles of 0° to 90° RAO. The differences for other organs do not vary as much and is only about 10% for the brain. For a LCI-High CBCT protocol, the difference between mean and mean ± 1 SD head size is about 100% for lens dose and only 10% for mean and peak brain dose; the difference between 20 and 3 year-old mean head size is an increase of about 200% for the eye lens dose and only 30% for mean and peak brain dose. Dose for all organs increases with decreasing head size for the same reference point air kerma. These results will allow size-specific dose estimates to be made using software such as our dose tracking system (DTS).

Assessment of organ and effective dose when using region-of-interest attenuators in cone-beam CT and interventional fluoroscopy

In some medical-imaging procedures using cone-beam CT (CBCT) and fluoroscopy, only the center of the field of view (FOV) may be needed to be visualized with optimal image quality. To reduce the dose to the patient while maintaining visualization of the entire FOV, a Cu attenuator with a circular aperture for the region of interest (ROI) is used. The potential organ and effective dose reductions of ROI imaging when applied to CBCT and interventional fluoroscopic procedures were determined using EGSnrc Monte Carlo code. The Monte Carlo model was first validated by comparing the surface dose distribution in a solid-water block phantom with measurement by Gafchromic film. The dependence of dose reduction on the ROI attenuator thickness, the opening size of the ROI, the axial beam position, and the location of the different organs for both neuro and thoracic imaging was evaluated. The results showed a reduction in most organ doses of 45% to 70% and in effective dose of 46% to 66% compared to the dose in a CBCT scan and in an interventional procedure without the ROI attenuator. This work provides evidence of a substantial reduction of organ and effective doses when using an ROI attenuator during CBCT and fluoroscopic procedures.