Does “Spreading” Skin Dose by Rotating the C-arm during an Intervention Work?

doi:10.1016/j.jvir.2010.12.025

Journal of Vascular and Interventional Radiology

Volume 22, Issue 4, April 2011, Pages 443-452

https://doi.org/10.1016/j.jvir.2010.12.025 Get rights and content

Abstract

Purpose

To determine if C-arm rotation is beneficial for reducing peak skin dose (PSD) in interventional radiology (IR) and, if so, under what circumstances.

Materials and Methods

The Monte Carlo method was used to perform ray tracing for detailed analyses of the effect of C-arm rotation on PSD across a range of patient sizes, C-arm configurations, and procedure types. Automatic dose-rate control curves on modern fluoroscopic systems were measured for input into the simulations.

Results

Rotating the C-arm to reduce the PSD is in most cases contraindicated and results in increased PSD when the C-arm is rotated from an original posteroanterior projection, in some cases resulting in a PSD increase by a factor of 5 or more. When prophylactic rotation was performed before a procedure, however, and the C-arm was rotated between opposed, distinct oblique angles, substantial reduction in PSD was achieved for patients of any size.

Conclusions

Rotating the C-arm during a procedure with the aim of “spreading” dose on the skin of the patient may not result in a reduction in PSD and may increase PSD. However, when used as a prophylactic measure combined with tight x-ray beam collimation, C-arm rotation can be used as a tool to reduce PSD. Tight collimation greatly increases the benefit of C-arm rotation.

Section snippets

Materials and Methods

A computational technique using the Monte Carlo method (20, 21, 22) was chosen for determining the effect of C-arm rotation on PSD in IR, owing to ease of implementation and utility for calculating data for many combinations of patient size, x-ray field size (ie, electronic magnification modes), and projection. The Monte Carlo method uses repeated random sampling to simulate physical events—in this case it was used to construct a ray-tracing engine to project a collimated x-ray beam onto a

Results

Owing to constraints of our study, the results presented apply only to IR and assume the use of good practice by the physician throughout the procedure. Representative examples of common scenarios are presented, and similar conclusions can be drawn for other permutations of electronic magnification mode and patient size. Also, in many of the following graphs, PSD is plotted as a function of increasing fluoroscopy time. However, PSD increases more rapidly when acquisition imaging is used, and

Discussion

The data presented in this article show that blindly rotating the C-arm to “spread” dose over a larger area of the skin may not reduce PSD in most cases and may increase PSD in some cases. When considered as a prophylactic measure and combined with tight collimation of the x-ray beam, however, C-arm rotation may be a useful tool to reduce PSD.

We can consider two cases. The first case concerns procedures where no prophylactic measures are taken to reduce PSD. The second case concerns procedures

Acknowledgments

The authors thank Sue Moreau for her editorial assistance.

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Geometry: The IRP is defined relative to the source not the patient, hence it does not account for angulation or table or patient position.6 Figure 7 shows a±40% effect for table height, while beam spreading by angulation can lower skin dose when combined with tight collimation.10 Tissue corrections: Correction factors (ie, air to tissue conversion and backscatter factors) are required to convert air kerma to tissue dose.
Fluoroscopically guided procedures are an area of radiology in which radiation exposure to the patient is highly operator dependent. Modern fluoroscopy machines display a variety of information, including technique factors, field of view, operating geometry, exposure mode, fluoroscopic time, air kerma at the reference point (RAK), and air kerma area-product. However, the presentation of this information is highly vendor specific, and many users are unaware of how to interpret this information and use it to perform a study with the minimum necessary dose. A conceptual framework for understanding the radiation dose readout during a procedure is to compare it to the dashboard of an automobile, where the rate at which radiation is being applied (the RAK rate [mGy/min]) is the dose “speed” and the cumulative amount of radiation applied (cumulative RAK [mGy]) is the dose “odometer.” This analogy can be used as a starting point to improve knowledge of these parameters, including how RAK is measured, how RAK correlates with skin dose, and how parameters are displayed differently during fluoroscopy and fluorography. Awareness of these factors is critical to understanding how dose parameters translate to patient risk and the consequences of high-dose studies. With this increased awareness, physicians performing fluoroscopically guided procedures can understand how to use built-in features of the fluoroscopic equipment (pulse rate, beam filtration, and automatic exposure control) and fluoroscopic techniques (procedure planning, patient positioning, proper collimation, and magnification) to reduce patient radiation dose, thereby improving patient safety.
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Radiation dose and operating factors were recorded for FGI performed in a hybrid room over a 16-month period. Cases exceeding 6 Gy RAK were investigated according to institutional policy. Information obtained from these investigations led to surgeon education focused on reducing patient dose. Points addressed included increasing table height, utilizing collimation and angulation, decreasing magnification modes, and maintaining minimal patient-to-detector distance. Procedural RAK doses and operating factors were compared 8 months pre- (group A) and 8 months post- (group B) educational intervention using analysis of variance with Tukey pairwise comparisons and t-tests. PSD distributions were calculated using custom software employing input data from fluoroscopic machine logs.
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: Poster presentation at the SIR 2010 Annual Meeting.

: Neither of the authors has identified a conflict of interest.

View full text

Laboratory investigationDoes “Spreading” Skin Dose by Rotating the C-arm during an Intervention Work?

Abstract

Purpose

Materials and Methods

Results

Conclusions

Section snippets

Materials and Methods

Results

Discussion

Acknowledgments

J Vasc Interv Radiol

J Vasc Interv Radiol

J Vasc Interv Radiol

J Vasc Interv Radiol

J Vasc Interv Radiol

J Am Coll Cardiol

J Vasc Interv Radiol

J Am Coll Cardiol

J Vasc Interv Radiol

J Vasc Interv Radiol

3D rotational angiography: the new gold standard in the detection of additional intracranial aneurysms

AJNR Am J Neuroradiol

Severe skin reactions from interventional fluoroscopy: case report and review of the literature

Radiology

Radiation-induced skin injuries from fluroscopy

Radiographics

Radiation injury from a fluoroscopic procedure

N Engl J Med

Dosimetric and radiation protection considerations based on some cases of patient skin injuries in interventional cardiology

Br J Radiol

Laboratory investigation
Does “Spreading” Skin Dose by Rotating the C-arm during an Intervention Work?